5,800 research outputs found
Non-Gaussian Component Analysis using Entropy Methods
Non-Gaussian component analysis (NGCA) is a problem in multidimensional data
analysis which, since its formulation in 2006, has attracted considerable
attention in statistics and machine learning. In this problem, we have a random
variable in -dimensional Euclidean space. There is an unknown subspace
of the -dimensional Euclidean space such that the orthogonal
projection of onto is standard multidimensional Gaussian and the
orthogonal projection of onto , the orthogonal complement
of , is non-Gaussian, in the sense that all its one-dimensional
marginals are different from the Gaussian in a certain metric defined in terms
of moments. The NGCA problem is to approximate the non-Gaussian subspace
given samples of .
Vectors in correspond to `interesting' directions, whereas
vectors in correspond to the directions where data is very noisy. The
most interesting applications of the NGCA model is for the case when the
magnitude of the noise is comparable to that of the true signal, a setting in
which traditional noise reduction techniques such as PCA don't apply directly.
NGCA is also related to dimension reduction and to other data analysis problems
such as ICA. NGCA-like problems have been studied in statistics for a long time
using techniques such as projection pursuit.
We give an algorithm that takes polynomial time in the dimension and has
an inverse polynomial dependence on the error parameter measuring the angle
distance between the non-Gaussian subspace and the subspace output by the
algorithm. Our algorithm is based on relative entropy as the contrast function
and fits under the projection pursuit framework. The techniques we develop for
analyzing our algorithm maybe of use for other related problems
Is Sensitivity to Anticoagulant Rodenticides Affected by Repeated Exposure in Hawks?
A seminal question in wildlife toxicology is whether exposure to an environmental contaminant, in particular a secondgeneration anticoagulant rodenticide, can evoke subtle long lasting effects on body condition, physiological function and survival. Many reports indicate that non-target predators often carry residues of several rodenticides, which is indicative of multiple exposures. An often-cited study in laboratory rats demonstrated that exposure to the second-generation anticoagulant rodenticide brodifacoum prolongs blood clotting time for a few days, but weeks later when rats were re-exposed to the first-generation anticoagulant rodenticide warfarin, coagulopathy was more pronounced in brodifacoum-treated rats than naïve rats exposed to warfarin. To further investigate this phenomenon, American kestrels were fed environmentally realistic doses of chlorophacinone or brodifacoum for a week, and following a week-long recovery period, birds were then challenged with a low-level dietary dose of chlorophacinone. In the present study, neither hematocrit nor clotting time (prothrombin time, Russell’s viper venom time) were differentially affected in sequentially exposed kestrels compared to naïve birds fed low-level dietary dose of chlorophacinone. While the present findings do not reveal lasting effects of anticoagulant exposure on blood clotting ability, findings in laboratory rats and other species have demonstrated such effects on blood clotting, and even other molecular pathways associated with immune function and xenobiotic metabolism. Additional studies using an environmentally realistic route of exposure and dose are underway to further test this hypothesis
Mental health issues in unaccompanied refugee minors
Previous studies about unaccompanied refugee minors (URMs) showed that they are a highly vulnerable group who have greater psychiatric morbidity than the general population. This review focuses on mental health issues among URMs. Articles in databases PsycINFO, Medline and PubMed from 1998 to 2008 addressing this topic were reviewed. The literature had a considerable emphasis on the assessment of PTSD symptoms. Results revealed higher levels of PTSD symptoms in comparison to the norm populations and accompanied refugee minors. In several studies, age and female gender predicted or influenced PTSD symptoms. The existing literature only permits limited conclusions on this very hard to reach population. Future research should include the analysis of long-term outcomes, stress management and a more thorough analysis of the whole range of psychopathology. Additionally, the development of culturally sensitive norms and standardized measures for diverse ethnic groups is of great importance
On Power Law Inflation in DBI Models
Inflationary models in string theory which identify the inflaton with an open
string modulus lead to effective field theories with non-canonical kinetic
terms: Dirac-Born-Infeld scalar field theories. In the case of a -brane
moving in an AdS throat with a quadratic scalar field potential DBI kinetic
terms allow a novel realization of power law inflation. This note adresses the
question of whether this behaviour is special to this particular choice of
throat geometry and potential. The answer is that for any throat geometry one
can explicitly find a potential which leads to power law inflation. This
generalizes the well known fact that an exponential potential gives power law
inflation in the case of canonical kinetic terms.Comment: References and comments adde
Low dose influenza virus challenge in the ferret leads to increased virus shedding and greater sensitivity to oseltamivir
Ferrets are widely used to study human influenza virus infection. Their airway physiology and cell receptor distribution makes them ideal for the analysis of pathogenesis and virus transmission, and for testing the efficacy of anti-influenza interventions and vaccines. The 2009 pandemic influenza virus (H1N1pdm09) induces mild to moderate respiratory disease in infected ferrets, following inoculation with 106 plaque-forming units (pfu) of virus. We have demonstrated that reducing the challenge dose to 102 pfu delays the onset of clinical signs by 1 day, and results in a modest reduction in clinical signs, and a less rapid nasal cavity innate immune response. There was also a delay in virus production in the upper respiratory tract, this was up to 9-fold greater and virus shedding was prolonged. Progression of infection to the lower respiratory tract was not noticeably delayed by the reduction in virus challenge. A dose of 104 pfu gave an infection that was intermediate between those of the 106 pfu and 102 pfu doses. To address the hypothesis that using a more authentic low challenge dose would facilitate a more sensitive model for antiviral efficacy, we used the well-known neuraminidase inhibitor, oseltamivir. Oseltamivir-treated and untreated ferrets were challenged with high (106 pfu) and low (102 pfu) doses of influenza H1N1pdm09 virus. The low dose treated ferrets showed significant delays in innate immune response and virus shedding, delayed onset of pathological changes in the nasal cavity, and reduced pathological changes and viral RNA load in the lung, relative to untreated ferrets. Importantly, these observations were not seen in treated animals when the high dose challenge was used. In summary, low dose challenge gives a disease that more closely parallels the disease parameters of human influenza infection, and provides an improved pre-clinical model for the assessment of influenza therapeutics, and potentially, influenza vaccines
Inter- and Intragranular Effects in Superconducting Compacted Platinum Powders
Compacted platinum powders exhibit a sharp onset of diamagnetic screening at
mK in zero magnetic field in all samples investigated. This
sharp onset is interpreted in terms of the intragranular transition into the
superconducting state. At lower temperatures, the magnetic ac susceptibility
strongly depends on the ac field amplitude and reflects the small intergranular
critical current density . This critical current density shows a strong
dependence on the packing fraction f of the granular samples. Surprisingly,
increases significantly with decreasing f ( A/cm for f = 0.67 and A/cm for f
= 0.50). The temperature dependence of shows strong positive curvature
over a wide temperature range for both samples. The phase diagrams of inter-
and intragranular superconductivity for different samples indicate that the
granular structure might play the key role for an understanding of the origin
of superconductivity in the platinum compacts.Comment: 11 pages including 9 figures. To appear in Phys. Rev. B in Nov. 0
Pricing in inflationary times: The penny drops
How does the frequency and magnitude of micro-price rises and falls relate to macroeconomic crisis, as well as moderation? Weekly micropricing behaviour in British groceries was investigated across three leading retailers over the moderation period 2004–7 and the crisis period 2008–10. We find significant price flexibility sharply distinguished from behaviour observed in most previous works. Downward price flexibility increased markedly in 2008. Overall basket prices rise, but significantly more individual prices fall than rise in the latter period. Tests of obfuscation in price setting suggested that large numbers of small price falls were used to disguise the basket price rises
Superconducting properties of RuSr2GdCu2O8 studied by SQUID magnetometry
For polycrystalline RuSr2GdCu2O8 (Ru-1212), distinct peaks have been reported
in d.c. magnetization in the superconducting state of the sample. Sr2GdRuO6
(Sr-2116), the precursor for the preparation of Ru-1212, shows similar peaks in
the same temperature regime. Based on measurements performed on both bulk and
powdered samples of Ru-1212 and Sr-2116, we exclude the possibility, that the
observed behavior of the magnetization of Ru-1212 is due to Sr-2116 impurities.
The effect is related to the superconductivity of Ru-1212, but it is not an
intrinsic property of this compound. We provide evidence that the observation
of magnetization peaks in the superconducting state of Ru-1212 is due to flux
motion generated by the movement of the sample in an inhomogeneous field,
during the measurement in the SQUID magnetometer. We propose several tests,
that help to decide, whether the features observed in a SQUID magnetization
measurement of Ru-1212 represent a property of the compound or not.Comment: 22 pages, 9 figure
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