4,252 research outputs found
Universally Sloppy Parameter Sensitivities in Systems Biology
Quantitative computational models play an increasingly important role in
modern biology. Such models typically involve many free parameters, and
assigning their values is often a substantial obstacle to model development.
Directly measuring \emph{in vivo} biochemical parameters is difficult, and
collectively fitting them to other data often yields large parameter
uncertainties. Nevertheless, in earlier work we showed in a
growth-factor-signaling model that collective fitting could yield
well-constrained predictions, even when it left individual parameters very
poorly constrained. We also showed that the model had a `sloppy' spectrum of
parameter sensitivities, with eigenvalues roughly evenly distributed over many
decades. Here we use a collection of models from the literature to test whether
such sloppy spectra are common in systems biology. Strikingly, we find that
every model we examine has a sloppy spectrum of sensitivities. We also test
several consequences of this sloppiness for building predictive models. In
particular, sloppiness suggests that collective fits to even large amounts of
ideal time-series data will often leave many parameters poorly constrained.
Tests over our model collection are consistent with this suggestion. This
difficulty with collective fits may seem to argue for direct parameter
measurements, but sloppiness also implies that such measurements must be
formidably precise and complete to usefully constrain many model predictions.
We confirm this implication in our signaling model. Our results suggest that
sloppy sensitivity spectra are universal in systems biology models. The
prevalence of sloppiness highlights the power of collective fits and suggests
that modelers should focus on predictions rather than on parameters.Comment: Submitted to PLoS Computational Biology. Supplementary Information
available in "Other Formats" bundle. Discussion slightly revised to add
historical contex
Dendritic cell nediated inhibition of lentiviral infection
Lentiviral entry to quiescent lymphocytes represents a 'time bomb' waiting for cellular activation to spread infection. In order to undergo immune activation T cells interact with dendritic cells presenting peptide:MHC complexes 'sampling' them to look for agonist peptides and receiving survival signals from self peptides. This makes the dendritic cell:T cell interaction an ideal checkpoint to contain lentiviral infection of quiescent lypmhocytes
Interleukins 7 and 15 Maintain Human T Cell Proliferative Capacity through STAT5 Signaling
T lymphocytes require signals from self-peptides and cytokines, most notably interleukins 7 and 15 (IL-7, IL-15), for survival. While mouse T cells die rapidly if IL-7 or IL-15 is withdrawn, human T cells can survive prolonged withdrawal of IL-7 and IL-15. Here we show that IL-7 and IL-15 are required to maintain human T cell proliferative capacity through the STAT5 signaling pathway. T cells from humanized mice proliferate better if stimulated in the presence of human IL-7 or IL-15 or if T cells are exposed to human IL-7 or IL-15 in mice. Freshly isolated T cells from human peripheral blood lose proliferative capacity if cultured for 24 hours in the absence of IL-7 or IL-15. We further show that phosphorylation of STAT5 correlates with proliferation and inhibition of STAT5 reduces proliferation. These results reveal a novel role of IL-7 and IL-15 in maintaining human T cell function, provide an explanation for T cell dysfunction in humanized mice, and have significant implications for in vitro studies with human T cells
Financial Incentives and Physician Practice Participation in Medicare’s Value‐Based Reforms
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145327/1/hesr12743_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145327/2/hesr12743-sup-0001-AppendixSA1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145327/3/hesr12743.pd
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Virtual Surgical Planning in Subscapular System Free Flap Reconstruction of Midface Defects.
OBJECTIVES: Reconstruction of the midface has many inherent challenges, including orbital support, skull base reconstruction, optimizing midface projection, separation of the nasal cavity and dental rehabilitation. Subscapular system free flaps (SF) have sufficient bone stock to support complex reconstruction and the option of separate soft tissue components. This study analyzes the effect of virtual surgical planning (VSP) in SF for midface on subsite reconstruction, bone segment contact and anatomic position.
MATERIALS AND METHODS: Retrospective cohort of patients with midface defects that underwent SF reconstruction at a single tertiary care institution.
RESULTS: Nine cases with VSP were compared to fourteen cases without VSP. VSP was associated with a higher number of successfully reconstructed subunits (5.9 vs 4.2, 95% CI of mean difference 0.31-3.04, p = 0.018), a higher number of successful bony contact between segments (2.2 vs 1.4, 95% CI of mean difference 0.0-1.6, p = 0.050), and a higher percent of segments in anatomic position (100% vs 71%, 95% CI of mean difference 2-55%, p = 0.035). When postoperative bone position after VSP reconstruction was compared to preoperative scans, the difference in anteroposterior, vertical and lateral projection compared to the preoperative \u27ideal\u27 bone position was82% of measurements. There were no flap losses.
CONCLUSION: VSP may augment SF reconstruction of the midface by allowing for improved subunit reconstruction, bony segment contact and anatomically correct bone segment positioning. VSP can be a useful adjunct for complex midface reconstruction and the benefits should be weighed against cost
On the relation between the Feynman paradox and Aharonov-Bohm effects
The magnetic Aharonov-Bohm (A-B) effect occurs when a point charge interacts
with a line of magnetic flux, while its dual, the Aharonov-Casher (A-C) effect,
occurs when a magnetic moment interacts with a line of charge. For the two
interacting parts of these physical systems, the equations of motion are
discussed in this paper. The generally accepted claim is that both parts of
these systems do not accelerate, while Boyer has claimed that both parts of
these systems do accelerate. Using the Euler-Lagrange equations we predict that
in the case of unconstrained motion only one part of each system accelerates,
while momentum remains conserved. This prediction requires a time dependent
electromagnetic momentum. For our analysis of unconstrained motion the A-B
effects are then examples of the Feynman paradox. In the case of constrained
motion, the Euler-Lagrange equations give no forces in agreement with the
generally accepted analysis. The quantum mechanical A-B and A-C phase shifts
are independent of the treatment of constraint. Nevertheless, experimental
testing of the above ideas and further understanding of A-B effects which is
central to both quantum mechanics and electromagnetism may be possible.Comment: 21 pages, 5 figures, recently submitted to New Journal of Physic
The role of P-wave inelasticity in J/psi to pi+pi-pi0
We discuss the importance of inelasticity in the P-wave pi pi amplitude on
the Dalitz distribution of 3pi events in J/psi decay. The inelasticity, which
becomes sizable for pi pi masses above 1.4 GeV, is attributed to
KK to pi pi rescattering. We construct an analytical model for the
two-channel scattering amplitude and use it to solve the dispersion relation
for the isobar amplitudes that parametrize the J/psi decay. We present
comparisons between theoretical predictions for the Dalitz distribution of 3pi
events with available experimental data.Comment: 10 pages, 10 figure
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