Inapproximability of Truthful Mechanisms via Generalizations of the VC Dimension

Algorithmic mechanism design (AMD) studies the delicate interplay between computational efficiency, truthfulness, and optimality. We focus on AMD's paradigmatic problem: combinatorial auctions. We present a new generalization of the VC dimension to multivalued collections of functions, which encompasses the classical VC dimension, Natarajan dimension, and Steele dimension. We present a corresponding generalization of the Sauer-Shelah Lemma and harness this VC machinery to establish inapproximability results for deterministic truthful mechanisms. Our results essentially unify all inapproximability results for deterministic truthful mechanisms for combinatorial auctions to date and establish new separation gaps between truthful and non-truthful algorithms

Learning Geometric Concepts with Nasty Noise

We study the efficient learnability of geometric concept classes - specifically, low-degree polynomial threshold functions (PTFs) and intersections of halfspaces - when a fraction of the data is adversarially corrupted. We give the first polynomial-time PAC learning algorithms for these concept classes with dimension-independent error guarantees in the presence of nasty noise under the Gaussian distribution. In the nasty noise model, an omniscient adversary can arbitrarily corrupt a small fraction of both the unlabeled data points and their labels. This model generalizes well-studied noise models, including the malicious noise model and the agnostic (adversarial label noise) model. Prior to our work, the only concept class for which efficient malicious learning algorithms were known was the class of origin-centered halfspaces. Specifically, our robust learning algorithm for low-degree PTFs succeeds under a number of tame distributions -- including the Gaussian distribution and, more generally, any log-concave distribution with (approximately) known low-degree moments. For LTFs under the Gaussian distribution, we give a polynomial-time algorithm that achieves error $O(\epsilon)$, where $\epsilon$ is the noise rate. At the core of our PAC learning results is an efficient algorithm to approximate the low-degree Chow-parameters of any bounded function in the presence of nasty noise. To achieve this, we employ an iterative spectral method for outlier detection and removal, inspired by recent work in robust unsupervised learning. Our aforementioned algorithm succeeds for a range of distributions satisfying mild concentration bounds and moment assumptions. The correctness of our robust learning algorithm for intersections of halfspaces makes essential use of a novel robust inverse independence lemma that may be of broader interest

From average case complexity to improper learning complexity

The basic problem in the PAC model of computational learning theory is to determine which hypothesis classes are efficiently learnable. There is presently a dearth of results showing hardness of learning problems. Moreover, the existing lower bounds fall short of the best known algorithms. The biggest challenge in proving complexity results is to establish hardness of {\em improper learning} (a.k.a. representation independent learning).The difficulty in proving lower bounds for improper learning is that the standard reductions from $\mathbf{NP}$-hard problems do not seem to apply in this context. There is essentially only one known approach to proving lower bounds on improper learning. It was initiated in (Kearns and Valiant 89) and relies on cryptographic assumptions. We introduce a new technique for proving hardness of improper learning, based on reductions from problems that are hard on average. We put forward a (fairly strong) generalization of Feige's assumption (Feige 02) about the complexity of refuting random constraint satisfaction problems. Combining this assumption with our new technique yields far reaching implications. In particular, 1. Learning $\mathrm{DNF}$'s is hard. 2. Agnostically learning halfspaces with a constant approximation ratio is hard. 3. Learning an intersection of $\omega(1)$ halfspaces is hard.Comment: 34 page

Full three-dimensional isotropic carpet cloak designed by quasi-conformal transformation optics

A fully three-dimensional carpet cloak presenting invisibility in all viewing angles is theoretically demonstrated. The design is developed using transformation optics and threedimensional quasi-conformal mapping. Parametrization strategy and numerical optimization of the coordinate transformation deploying a quasi-Newton method is applied. A discussion about the minimum achievable anisotropy in the 3D transformation optics is presented. The method allows to reduce the anisotropy in the cloak and an isotropic medium could be considered. Numerical simulations confirm the strategy employed enabling the design of an isotropic reflectionless broadband carpet cloak independently of the incident light direction and polarization25192351723522CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGnão temnão temnão te

Zika virus tropism and interactions in myelinating neural cell cultures: CNS cells and myelin are preferentially affected

The recent global outbreak of Zika virus (ZIKV) infection has been linked to severe neurological disorders affecting the peripheral and central nervous systems (PNS and CNS, respectively). The pathobiology underlying these diverse clinical phenotypes are the subject of intense research; however, even the principal neural cell types vulnerable to productive Zika infection remain poorly characterised. Here we used CNS and PNS myelinating cultures from wild type and Ifnar1 knockout mice to examine neuronal and glial tropism and short-term consequences of direct infection with a Brazilian variant of ZIKV. Cell cultures were infected pre- or post-myelination for various intervals, then stained with cell-type and ZIKV-specific antibodies. In bypassing systemic immunity using ex vivo culture, and the type I interferon response in Ifnar1 deficient cells, we were able to evaluate the intrinsic infectivity of neural cells. Through systematic quantification of ZIKV infected cells in myelinating cultures, we found that ZIKV infection is enhanced in the absence of the type I interferon responses and that CNS cells are considerably more susceptible to infection than PNS cells. In particular, we demonstrate that CNS axons and myelinating oligodendrocytes are especially vulnerable to injury. These results have implications for understanding the pathobiology of neurological symptoms associated with ZIKV infection. Furthermore, we provide a quantifiable ex vivo infection model that can be used for fundamental and therapeutic studies on viral neuroinvasion and its consequences

Seasonal effects on HPLC-DAD-UV and UPLC-ESI-MS fingerprints and analgesic activities of vernonia condensata baker extracts

Vernonia condensata Baker leaves have different uses in Brazilian folk medicine, including as analgesic and anti-inflammatory agents. The purpose of this study was to evaluate the seasonal effects on their high performance liquid chromatography with a diode array detector (HPLC-DAD-UV) and ultra-performance liquid chromatography coupled to a mass spectrometer with an electrospray interface (UPLC-ESI-MS) fingerprints, as well as their analgesic activities in mice. There were significant seasonal effects on the relative abundances of the metabolites of the V. condensate leaves as well as on their activities. Analgesic activities in the writhing test were observed with the polar fraction of the leaf extracts collected in autumn, winter and summer (400 mg kg(-1)); and with the intermediate fraction of leaves collected in autumn (25 and 400 mg kg(-1)) and in the summer (100 mg kg(-1)). In conclusion, the results confirm peripherally-mediated anti-inflammatory and analgesic activities for V. condensata leaves and suggest that these are influenced by the harvesting season. N-oxides alkaloids as well as vernonioside play important roles in determining this activity262350358CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFundacao Araucari

Identificação do nível de conhecimento básico de alunos da 5º serie do ensino fundamental acerca do uso consciente de água.

..

Ribonucleoprotein Particles Containing Non-Coding Y RNAs, Ro60, La and Nucleolin Are Not Required for Y RNA Function in DNA Replication

BACKGROUND: Ro ribonucleoprotein particles (Ro RNPs) consist of a non-coding Y RNA bound by Ro60, La and possibly other proteins. The physiological function of Ro RNPs is controversial as divergent functions have been reported for its different constituents. We have recently shown that Y RNAs are essential for the initiation of mammalian chromosomal DNA replication, whereas Ro RNPs are implicated in RNA stability and RNA quality control. Therefore, we investigate here the functional consequences of RNP formation between Ro60, La and nucleolin proteins with hY RNAs for human chromosomal DNA replication. METHODOLOGY/PRINCIPAL FINDINGS: We first immunoprecipitated Ro60, La and nucleolin together with associated hY RNAs from HeLa cytosolic cell extract, and analysed the protein and RNA compositions of these precipitated RNPs by Western blotting and quantitative RT-PCR. We found that Y RNAs exist in several RNP complexes. One RNP comprises Ro60, La and hY RNA, and a different RNP comprises nucleolin and hY RNA. In addition about 50% of the Y RNAs in the extract are present outside of these two RNPs. Next, we immunodepleted these RNP complexes from the cytosolic extract and tested the ability of the depleted extracts to reconstitute DNA replication in a human cell-free system. We found that depletion of these RNP complexes from the cytosolic extract does not inhibit DNA replication in vitro. Finally, we tested if an excess of recombinant pure Ro or La protein inhibits Y RNA-dependent DNA replication in this cell-free system. We found that Ro60 and La proteins do not inhibit DNA replication in vitro. CONCLUSIONS/SIGNIFICANCE: We conclude that RNPs containing hY RNAs and Ro60, La or nucleolin are not required for the function of hY RNAs in chromosomal DNA replication in a human cell-free system, which can be mediated by Y RNAs outside of these RNPs. These data suggest that Y RNAs can support different cellular functions depending on associated proteins