7,651 research outputs found
The challenge of high capital inflows to financial stability: an emerging market perspective.
High liquidity and continued economic weakness in advanced economies have led to a surge in capital flows to emerging markets with strong fundamentals and open financial accounts such as Brazil. While capital inflows have undeniable benefits to emerging economies, they are also potentially destabilising. Past experience has shown that high levels of capital inflows can lead to exchange rate volatility and credit or asset price bubbles. In the context of Brazil’s inflation-targeting regime for monetary policy, macroprudential measures have proved to be a useful complement to traditional macroeconomic policies. However, today’s imbalanced global economy presents an especially difficult challenge for policymakers. The international financial community needs to work together on two fronts: improving our macroprudential toolkit and building a stronger framework for multilateral macroeconomic cooperation.
On Pruning for Score-Based Bayesian Network Structure Learning
Many algorithms for score-based Bayesian network structure learning (BNSL),
in particular exact ones, take as input a collection of potentially optimal
parent sets for each variable in the data. Constructing such collections
naively is computationally intensive since the number of parent sets grows
exponentially with the number of variables. Thus, pruning techniques are not
only desirable but essential. While good pruning rules exist for the Bayesian
Information Criterion (BIC), current results for the Bayesian Dirichlet
equivalent uniform (BDeu) score reduce the search space very modestly,
hampering the use of the (often preferred) BDeu. We derive new non-trivial
theoretical upper bounds for the BDeu score that considerably improve on the
state-of-the-art. Since the new bounds are mathematically proven to be tighter
than previous ones and at little extra computational cost, they are a promising
addition to BNSL methods
Topological insulator particles as optically induced oscillators: towards dynamical force measurements and optical rheology
We report the first experimental study upon the optical trapping and
manipulation of topological insulator (TI) particles. By virtue of the unique
TI properties, which have a conducting surface and an insulating bulk, the
particles present a peculiar behaviour in the presence of a single laser beam
optical tweezers: they oscillate in a plane perpendicular to the direction of
the laser propagation, as a result of the competition between radiation
pressure and gradient forces. In other words, TI particles behave as optically
induced oscillators, allowing dynamical measurements with unprecedented
simplicity and purely optical control. Actually, optical rheology of soft
matter interfaces and biological membranes, as well as dynamical force
measurements in macromolecules and biopolymers, may be quoted as feasible
possibilities for the near future.Comment: 6 pages, 5 figures. Correspondence and requests for Supplementary
Material should be addressed to [email protected]
Joints in Random Forests
Decision Trees (DTs) and Random Forests (RFs) are powerful discriminative
learners and tools of central importance to the everyday machine learning
practitioner and data scientist. Due to their discriminative nature, however,
they lack principled methods to process inputs with missing features or to
detect outliers, which requires pairing them with imputation techniques or a
separate generative model. In this paper, we demonstrate that DTs and RFs can
naturally be interpreted as generative models, by drawing a connection to
Probabilistic Circuits, a prominent class of tractable probabilistic models.
This reinterpretation equips them with a full joint distribution over the
feature space and leads to Generative Decision Trees (GeDTs) and Generative
Forests (GeFs), a family of novel hybrid generative-discriminative models. This
family of models retains the overall characteristics of DTs and RFs while
additionally being able to handle missing features by means of marginalisation.
Under certain assumptions, frequently made for Bayes consistency results, we
show that consistency in GeDTs and GeFs extend to any pattern of missing input
features, if missing at random. Empirically, we show that our models often
outperform common routines to treat missing data, such as K-nearest neighbour
imputation, and moreover, that our models can naturally detect outliers by
monitoring the marginal probability of input features
Metallochaperones Are Needed for Mycobacterium tuberculosis and Escherichia coli Nicotinamidase-Pyrazinamidase Activity.
Mycobacterium tuberculosis nicotinamidase-pyrazinamidase (PZAse) is a metalloenzyme that catalyzes conversion of nicotinamide-pyrazinamide to nicotinic acid-pyrazinoic acid. This study investigated whether a metallochaperone is required for optimal PZAse activity. M. tuberculosis and Escherichia coli PZAses (PZAse-MT and PZAse-EC, respectively) were inactivated by metal depletion (giving PZAse-MT-Apo and PZAse-EC-Apo). Reactivation with the E. coli metallochaperone ZnuA or Rv2059 (the M. tuberculosis analog) was measured. This was repeated following proteolytic and thermal treatment of ZnuA and Rv2059. The CDC1551 M. tuberculosis reference strain had the Rv2059 coding gene knocked out, and PZA susceptibility and the pyrazinoic acid (POA) efflux rate were measured. ZnuA (200 μM) achieved 65% PZAse-EC-Apo reactivation. Rv2059 (1 μM) and ZnuA (1 μM) achieved 69% and 34.3% PZAse-MT-Apo reactivation, respectively. Proteolytic treatment of ZnuA and Rv2059 and application of three (but not one) thermal shocks to ZnuA significantly reduced the capacity to reactivate PZAse-MT-Apo. An M. tuberculosis Rv2059 knockout strain was Wayne positive and susceptible to PZA and did not have a significantly different POA efflux rate than the reference strain, although a trend toward a lower efflux rate was observed after knockout. The metallochaperone Rv2059 restored the activity of metal-depleted PZAse in vitro Although Rv2059 is important in vitro, it seems to have a smaller effect on PZA susceptibility in vivo. It may be important to mechanisms of action and resistance to pyrazinamide in M. tuberculosis Further studies are needed for confirmation.IMPORTANCE Tuberculosis is an infectious disease caused by the bacterium Mycobacterium tuberculosis and remains one of the major causes of disease and death worldwide. Pyrazinamide is a key drug used in the treatment of tuberculosis, yet its mechanism of action is not fully understood, and testing strains of M. tuberculosis for pyrazinamide resistance is not easy with the tools that are presently available. The significance of the present research is that a metallochaperone-like protein may be crucial to pyrazinamide's mechanisms of action and of resistance. This may support the development of improved tools to detect pyrazinamide resistance, which would have significant implications for the clinical management of patients with tuberculosis: drug regimens that are appropriately tailored to the resistance profile of a patient's individual strain lead to better clinical outcomes, reduced onward transmission of infection, and reduction of the development of resistant strains that are more challenging and expensive to treat
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