353 research outputs found
Generalized Permutohedra from Probabilistic Graphical Models
A graphical model encodes conditional independence relations via the Markov
properties. For an undirected graph these conditional independence relations
can be represented by a simple polytope known as the graph associahedron, which
can be constructed as a Minkowski sum of standard simplices. There is an
analogous polytope for conditional independence relations coming from a regular
Gaussian model, and it can be defined using multiinformation or relative
entropy. For directed acyclic graphical models and also for mixed graphical
models containing undirected, directed and bidirected edges, we give a
construction of this polytope, up to equivalence of normal fans, as a Minkowski
sum of matroid polytopes. Finally, we apply this geometric insight to construct
a new ordering-based search algorithm for causal inference via directed acyclic
graphical models.Comment: Appendix B is expanded. Final version to appear in SIAM J. Discrete
Mat
Enhancement of cancer chemotherapy in vitro by intense ultrawideband electric field pulses
Experiments have been performed to enhance the Jurkat cell-killing effects of the cancer chemotherapy agent bleomycin using electric field pulses of 50â200âkV/cm50â200kVâcm peak electric field strength, ⌠150ânsâŒ150ns duration, and nanosecond rise time. Dramatic increases in cell killing (factors of ⌠1000âŒ1000) were observed with a low dose of bleomycin after treatment with trains of ten or more pulses at all electric field strengths tested, compared to pulse-only or drug-only treatments. Cell death occurred within 24âh24h for treated cells, with some evidence of membrane phosphatidylserine externalization at 6âh6h postexposure but no significant increase in caspase activity, indicating that the primary mode of cell death was not caspase-mediated apoptosis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87477/2/094701_1.pd
Differentially Private Model Selection with Penalized and Constrained Likelihood
In statistical disclosure control, the goal of data analysis is twofold: The
released information must provide accurate and useful statistics about the
underlying population of interest, while minimizing the potential for an
individual record to be identified. In recent years, the notion of differential
privacy has received much attention in theoretical computer science, machine
learning, and statistics. It provides a rigorous and strong notion of
protection for individuals' sensitive information. A fundamental question is
how to incorporate differential privacy into traditional statistical inference
procedures. In this paper we study model selection in multivariate linear
regression under the constraint of differential privacy. We show that model
selection procedures based on penalized least squares or likelihood can be made
differentially private by a combination of regularization and randomization,
and propose two algorithms to do so. We show that our private procedures are
consistent under essentially the same conditions as the corresponding
non-private procedures. We also find that under differential privacy, the
procedure becomes more sensitive to the tuning parameters. We illustrate and
evaluate our method using simulation studies and two real data examples
Phosphatidylinositol 3âkinase and Akt effectors mediate insulinâlike growth factorâI neuroprotection in dorsal root ganglia neurons
Insulinâlike growth factorâI (IGFâI) protects neurons of the peripheral nervous system from apoptosis, but the underlying signaling pathways are not well understood. We studied IGFâI mediated signaling in embryonic dorsal root ganglia (DRG) neurons. DRG neurons express IGFâI receptors (IGFâIR), and IGFâI activates the phosphatidylinositol 3âkinase (PI3K)/Akt pathway. High glucose exposure induces apoptosis, which is inhibited by IGFâI through the PI3K/Akt pathway. IGFâI stimulation of the PI3K/Akt pathway phosphorylates three known Akt effectors: the survival transcription factor cyclic AMP response element binding protein (CREB) and the proâapoptotic effector proteins glycogen synthase kinaseâ3ÎČ (GSKâ3ÎČ) and forkhead (FKHR). IGFâI regulates survival at the nuclear level through accumulation of phosphoâAkt in DRG neuronal nuclei, increased CREBâmediated transcription, and nuclear exclusion of FKHR. High glucose increases expression of the proâapoptotic Bcl protein Bim (a transcriptional target of FKHR). However, IGFâI does not regulate Bim or antiâapoptotic BclâxL protein expression levels, which suggests that IGFâI neuroprotection is not through regulation of their expression. High glucose also induces loss of the initiator caspaseâ9 and increases caspaseâ3 cleavage, effects blocked by IGFâI. These data suggest that IGFâI prevents apoptosis in DRG neurons by regulating PI3K/Akt pathway effectors, including GSKâ3ÎČ, CREB, and FKHR, and by blocking caspase activation.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154325/1/fsb2fj041581fje.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154325/2/fsb2fj041581fje-sup-0001.pd
Pionic Deuterium
The strong interaction shift and broadening in pionic deuterium have been
remeasured with high statistics by means of the (3p-1s) X-ray transition using
the cyclotron trap and a high-resolution crystal spectrometer. Preliminary
results are (-2325+/-31) meV (repulsive) for the shift and (1171+23/-49} meV
for the width, which yields precise values for the pion-deuteron scattering
length and the threshold parameter for pion production.Comment: Conf. Proc. Few Body 19 (FB19), August 31 - September 5, 2009, Bonn,
Germany 9 pages, 13 figure
Incorporating spatial dependence into a multicellular tumor spheroid growth model
Recent models for organism and tumor growth yield simple scaling laws based on conservation of energy. Here, we extend such a model to include spatial dependence to model necrotic core formation. We adopt the allometric equation for tumor volume with a reaction-diffusion equation for nutrient concentration. In addition, we assume that the total metabolic energy and average cellular metabolic rate depend on nutrient concentration in a Michaelis-Menten-like manner. From experimental results, we relate the necrotic volume to nutrient consumption and estimate both the time and nutrient concentration at necrotic core formation. Based on experimental results, we demand that the necrotic core radius varies linearly with tumor radius after core formation and extend the equations for tumor volume and nutrient concentration to the postnecrotic core regime. In particular, we obtain excellent agreement with experimental data and the final steady-state viable rim thickness.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87333/2/124701_1.pd
Likelihood Geometry
We study the critical points of monomial functions over an algebraic subset
of the probability simplex. The number of critical points on the Zariski
closure is a topological invariant of that embedded projective variety, known
as its maximum likelihood degree. We present an introduction to this theory and
its statistical motivations. Many favorite objects from combinatorial algebraic
geometry are featured: toric varieties, A-discriminants, hyperplane
arrangements, Grassmannians, and determinantal varieties. Several new results
are included, especially on the likelihood correspondence and its bidegree.
These notes were written for the second author's lectures at the CIME-CIRM
summer course on Combinatorial Algebraic Geometry at Levico Terme in June 2013.Comment: 45 pages; minor changes and addition
On the driven Frenkel-Kontorova model: I. Uniform sliding states and dynamical domains of different particle densities
The dynamical behavior of a harmonic chain in a spatially periodic potential
(Frenkel-Kontorova model, discrete sine-Gordon equation) under the influence of
an external force and a velocity proportional damping is investigated. We do
this at zero temperature for long chains in a regime where inertia and damping
as well as the nearest-neighbor interaction and the potential are of the same
order. There are two types of regular sliding states: Uniform sliding states,
which are periodic solutions where all particles perform the same motion
shifted in time, and nonuniform sliding states, which are quasi-periodic
solutions where the system forms patterns of domains of different uniform
sliding states. We discuss the properties of this kind of pattern formation and
derive equations of motion for the slowly varying average particle density and
velocity. To observe these dynamical domains we suggest experiments with a
discrete ring of at least fifty Josephson junctions.Comment: Written in RevTeX, 9 figures in PostScrip
Floating oil-covered debris from Deepwater Horizon : identification and application
Author Posting. © IOP Publishing, 2012. This article is posted here by permission of IOP Publishing. Re-use is limited to non-commercial purposes. The definitive version was published in Environmental Research Letters 7 (2012): 015301, doi:10.1088/1748-9326/7/1/015301.The discovery of oiled and non-oiled honeycomb material in the Gulf of Mexico surface waters and along coastal beaches shortly after the explosion of Deepwater Horizon sparked debate about its origin and the oil covering it. We show that the unknown pieces of oiled and non-oiled honeycomb material collected in the Gulf of Mexico were pieces of the riser pipe buoyancy module of Deepwater Horizon. Biomarker ratios confirmed that the oil had originated from the Macondo oil well and had undergone significant weathering. Using the National Oceanic and Atmospheric Administration's records of the oil spill trajectory at the sea surface, we show that the honeycomb material preceded the front edge of the uncertainty of the oil slick trajectory by several kilometers. We conclude that the observation of debris fields deriving from damaged marine materials may be incorporated into emergency response efforts and forecasting of coastal impacts during future offshore oil spills, and ground truthing predicative models.This research was supported by NSF grant OCE-1043976 to CR
Making connections: technological interventions to support students in using, and tutors in creating, assessment feedback
This paper explores the potential of technology to enhance the assessment and feedback process for both staff and students. The âMaking Connectionsâ project aimed to better understand the connections that students make between the feedback that they receive and future assignments, and explored whether technology can help them in this activity. The project interviewed 10 tutors and 20 students, using a semi-structured approach. Data were analysed using a thematic approach, and the findings have identified a number of areas in which improvements could be made to the assessment and feedback process through the use of technology. The findings of the study cover each stage of the assessment process from the perspective of both staff and students. The findings are discussed in the context of current literature, and special attention is given to projects from the UK higher education sector intended to address the same issues.
Keywords: feed-forward; assessment; practices; technology; technology-enhanced learnin
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