1,060 research outputs found
Adaptive Hedge
Most methods for decision-theoretic online learning are based on the Hedge
algorithm, which takes a parameter called the learning rate. In most previous
analyses the learning rate was carefully tuned to obtain optimal worst-case
performance, leading to suboptimal performance on easy instances, for example
when there exists an action that is significantly better than all others. We
propose a new way of setting the learning rate, which adapts to the difficulty
of the learning problem: in the worst case our procedure still guarantees
optimal performance, but on easy instances it achieves much smaller regret. In
particular, our adaptive method achieves constant regret in a probabilistic
setting, when there exists an action that on average obtains strictly smaller
loss than all other actions. We also provide a simulation study comparing our
approach to existing methods.Comment: This is the full version of the paper with the same name that will
appear in Advances in Neural Information Processing Systems 24 (NIPS 2011),
2012. The two papers are identical, except that this version contains an
extra section of Additional Materia
Catching Up Faster by Switching Sooner: A Prequential Solution to the AIC-BIC Dilemma
Bayesian model averaging, model selection and its approximations such as BIC
are generally statistically consistent, but sometimes achieve slower rates og
convergence than other methods such as AIC and leave-one-out cross-validation.
On the other hand, these other methods can br inconsistent. We identify the
"catch-up phenomenon" as a novel explanation for the slow convergence of
Bayesian methods. Based on this analysis we define the switch distribution, a
modification of the Bayesian marginal distribution. We show that, under broad
conditions,model selection and prediction based on the switch distribution is
both consistent and achieves optimal convergence rates, thereby resolving the
AIC-BIC dilemma. The method is practical; we give an efficient implementation.
The switch distribution has a data compression interpretation, and can thus be
viewed as a "prequential" or MDL method; yet it is different from the MDL
methods that are usually considered in the literature. We compare the switch
distribution to Bayes factor model selection and leave-one-out
cross-validation.Comment: A preliminary version of a part of this paper appeared at the NIPS
2007 conferenc
Probability-free pricing of adjusted American lookbacks
Consider an American option that pays G(X^*_t) when exercised at time t,
where G is a positive increasing function, X^*_t := \sup_{s\le t}X_s, and X_s
is the price of the underlying security at time s. Assuming zero interest
rates, we show that the seller of this option can hedge his position by trading
in the underlying security if he begins with initial capital
X_0\int_{X_0}^{\infty}G(x)x^{-2}dx (and this is the smallest initial capital
that allows him to hedge his position). This leads to strategies for trading
that are always competitive both with a given strategy's current performance
and, to a somewhat lesser degree, with its best performance so far. It also
leads to methods of statistical testing that avoid sacrificing too much of the
maximum statistical significance that they achieve in the course of
accumulating data.Comment: 28 pages, 1 figur
Catching Up Faster by Switching Sooner: A Predictive Approach to Adaptive Estimation with an application to the AIC-BIC Dilemma
The diverse and unanticipated roles of Histone deacetylase 9 in coordinating plant development and environmental acclimation
Plants tightly control gene transcription to adapt to environmental conditions and steer growth and development. Different types of epigenetic modifications are instrumental in this. In recent years, an important role for the chromatin modifying RPD3/HDA1 class I HDAC HISTONE DEACETYLASE 9 (HDA9) emerged in the regulation of a multitude of plant traits and responses.
HDACs are widely considered transcriptional repressors and are typically part of multiprotein complexes containing co-repressors, DNA and histone binding proteins. By catalyzing the removal of acetyl groups from lysine residues of histone protein tails, HDA9 indeed negatively controls gene expression in many cases, in concert with interacting proteins such as POWERDRESS (PWR), HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15), WRKY53, ELONGATED HYPOCOTYL 5 (HY5), ABA INSENSITIVE 4 (ABI4) and EARLY FLOWERING 3 (ELF3). However, HDA9 activity has also been directly linked to transcriptional activation. In addition, following the recent breakthrough discovery of mutual negative feedback regulation between HDA9 and its interacting WRKY-domain transcription factor WRKY53, swift progress in gaining understanding of HDA9 biology is expected.
In this review, we summarize knowledge on this intriguing versatile – and long underrated – protein and propose novel leads to further unravel HDA9-governed molecular networks underlying plant development and environmental biology
Reinsertion of an inverted osteochondral lesion of the talus: A case report
Osteochondral lesions of the talus (OLTs) occur infrequently and are missed at the initial presentation in up to 67% of cases. Probably more than 1500 OLTs have been reported in published studies, of which, thus far, only 5 cases have been an inverted anterolateral OLT. An anterolateral OLT results from a hypersupination trauma, in which the talar dome is caught behind the fibula. Apparently, if the forces are large enough a " flip of the coin" phenomenon occurs, causing the fragment to invert 180° upside down. We present the case of a young female patient with an inverted OLT that was treated with open reduction and internal fixation using bioabsorbable pins. Follow-up radiographs and computed tomography showed a congruent joint and complete healing of the osteochondral fragment. At the short-term follow-up visit, the functional outcome was promising
Zfy genes are required for efficient meiotic sex chromosome inactivation (MSCI) in spermatocytes
During spermatogenesis, germ cells that fail to synapse their chromosomes or fail to undergo meiotic sex chromosome inactivation (MSCI) are eliminated via apoptosis during mid-pachytene. Previous work showed that Y-linked genes Zfy1 and Zfy2 act as "executioners" for this checkpoint, and that wrongful expression of either gene during pachytene triggers germ cell death. Here, we show that in mice, Zfy genes are also necessary for efficient MSCI and the sex chromosomes are not correctly silenced in Zfy-deficient spermatocytes. This unexpectedly reveals a triple role for Zfy at the mid-pachytene checkpoint in which Zfy genes first promote MSCI, then monitor its progress (since if MSCI is achieved, Zfy genes will be silenced), and finally execute cells with MSCI failure. This potentially constitutes a negative feedback loop governing this critical checkpoint mechanism
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