On measurement of top polarization as a probe of ttˉt \bar t production mechanisms at the LHC

In this note we demonstrate the use of top polarization in the study of $t \bar t$ resonances at the LHC, in the possible case where the dynamics implies a non-zero top polarization. As a probe of top polarization we construct an asymmetry in the decay-lepton azimuthal angle distribution (corresponding to the sign of $\cos\phi_\ell$) in the laboratory. The asymmetry is non-vanishing even for a symmetric collider like the LHC, where a positive $z$ axis is not uniquely defined. The angular distribution of the leptons has the advantage of being a faithful top-spin analyzer, unaffected by possible anomalous $tbW$ couplings, to linear order. We study, for purposes of demonstration, the case of a $Z'$ as might exist in the little Higgs models. We identify kinematic cuts which ensure that our asymmetry reflects the polarization in sign and magnitude. We investigate possibilities at the LHC with two energy options: $\sqrt{s} = 14$ TeV and $\sqrt{s} = 7$ TeV, as well as at the Tevatron. At the LHC the model predicts net top quark polarization of the order of a few per cent for $M_{Z'} \simeq 1200$ GeV, being as high as $10$ for a smaller mass of the $Z'$ of $700$ GeV and for the largest allowed coupling in the model, the values being higher for the $7$ TeV option. These polarizations translate to a deviation from the standard-model value of azimuthal asymmetry of up to about $4$ ($7$) for $14$ ($7$) TeV LHC, whereas for the Tevatron, values as high as $12$ are attained. For the $14$ TeV LHC with an integrated luminosity of 10 fb$^{-1}$, these numbers translate into a $3 \sigma$ sensitivity over a large part of the range $500 \lesssim M_{Z'} \lesssim 1500$ GeV.Comment: 28 page, LaTeX, requires JHEP style file, 12 figures. Typos corrected and references adde

A Critical Assessment of the Effects of Bt Transgenic Plants on Parasitoids

The ecological safety of transgenic insecticidal plants expressing crystal proteins (Cry toxins) from the bacterium Bacillus thuringiensis (Bt) continues to be debated. Much of the debate has focused on nontarget organisms, especially predators and parasitoids that help control populations of pest insects in many crops. Although many studies have been conducted on predators, few reports have examined parasitoids but some of them have reported negative impacts. None of the previous reports were able to clearly characterize the cause of the negative impact. In order to provide a critical assessment, we used a novel paradigm consisting of a strain of the insect pest, Plutella xylostella (herbivore), resistant to Cry1C and allowed it to feed on Bt plants and then become parasitized by Diadegma insulare, an important endoparasitoid of P. xylostella. Our results indicated that the parasitoid was exposed to a biologically active form of the Cy1C protein while in the host but was not harmed by such exposure. Parallel studies conducted with several commonly used insecticides indicated they significantly reduced parasitism rates on strains of P. xylostella resistant to these insecticides. These results provide the first clear evidence of the lack of hazard to a parasitoid by a Bt plant, compared to traditional insecticides, and describe a test to rigorously evaluate the risks Bt plants pose to predators and parasitoids

A Surprising Prevention Success: Why Did the HIV Epidemic Decline in Zimbabwe?

Daniel Halperin and colleagues examine reasons for the remarkable decline in HIV in Zimbabwe, in the context of severe social, political, and economic disruption

Color & Weak triplet scalars, the dimuon asymmetry in BsB_s decay, the top forward-backward asymmetry, and the CDF dijet excess

The new physics required to explain the anomalies recently reported by the D0 and CDF collaborations, namely the top forward-backward asymmetry (FBA), the like-sign dimuon charge asymmetry in semileptonic b decay, and the CDF dijet excess, has to feature an amount of flavor symmetry in order to satisfy the severe constrains arising from flavor violation. In this paper we show that, once baryon number conservation is imposed, color & weak triplet scalars with hypercharge $Y=1/3$ can feature the required flavor structure as a consequence of standard model gauge invariance. The color & weak triplet model can simultaneously explain the top FBA and the dimuon charge asymmetry or the dimuon charge asymmetry and the CDF dijet excess. However, the CDF dijet excess appears to be incompatible with the top FBA in the minimal framework. Our model for the dimuon asymmetry predicts the observed pattern $h_d\ll h_s$ in the region of parameter space required to explain the top FBA, whereas our model for the CDF dijet anomaly is characterized by the absence of beyond the SM b-quark jets in the excess region. Compatibility of the color & weak triplet with the electroweak constraints is also discussed. We show that a Higgs boson mass exceeding the LEP bound is typically favored in this scenario, and that both Higgs production and decay can be significantly altered by the triplet. The most promising collider signature is found if the splitting among the components of the triplet is of weak scale magnitude.Comment: references added, published versio

From presence to consciousness through virtual reality

Immersive virtual environments can break the deep, everyday connection between where our senses tell us we are and where we are actually located and whom we are with. The concept of 'presence' refers to the phenomenon of behaving and feeling as if we are in the virtual world created by computer displays. In this article, we argue that presence is worthy of study by neuroscientists, and that it might aid the study of perception and consciousness

The State of Research on Racial and Ethnic Discrimination in the Receipt of Health Care

https://ajph.aphapublications.org/doi/pdf/10.2105/AJPH.2012.30077

Automatic Physiological Waveform Processing for fMRI Noise Correction and Analysis

Functional MRI resting state and connectivity studies of brain focus on neural fluctuations at low frequencies which share power with physiological fluctuations originating from lung and heart. Due to the lack of automated software to process physiological signals collected at high magnetic fields, a gap exists in the processing pathway between the acquisition of physiological data and its use in fMRI software for both physiological noise correction and functional analyses of brain activation and connectivity. To fill this gap, we developed an open source, physiological signal processing program, called PhysioNoise, in the python language. We tested its automated processing algorithms and dynamic signal visualization on resting monkey cardiac and respiratory waveforms. PhysioNoise consistently identifies physiological fluctuations for fMRI noise correction and also generates covariates for subsequent analyses of brain activation and connectivity

Substrate docking to γ-secretase allows access of γ-secretase modulators to an allosteric site

γ-Secretase generates the peptides of Alzheimer's disease, Aβ40 and Aβ42, by cleaving the amyloid precursor protein within its transmembrane domain. γ-Secretase also cleaves numerous other substrates, raising concerns about γ-secretase inhibitor off-target effects. Another important class of drugs, γ-secretase modulators, alter the cleavage site of γ-secretase on amyloid precursor protein, changing the Aβ42/Aβ40 ratio, and are thus a promising therapeutic approach for Alzheimer's disease. However, the target for γ-secretase modulators is uncertain, with some data suggesting that they function on γ-secretase, whereas others support their binding to the amyloid precursor. In this paper we address this controversy by using a fluorescence resonance energy transfer-based assay to examine whether γ-secretase modulators alter Presenilin-1/γ-secretase conformation in intact cells in the absence of its natural substrates such as amyloid precursor protein and Notch. We report that the γ-secretase allosteric site is located within the γ-secretase complex, but substrate docking is needed for γ-secretase modulators to access this site

Twist1 Directly Regulates Genes That Promote Cell Proliferation and Migration in Developing Heart Valves

Twist1, a basic helix-loop-helix transcription factor, is expressed in mesenchymal precursor populations during embryogenesis and in metastatic cancer cells. In the developing heart, Twist1 is highly expressed in endocardial cushion (ECC) valve mesenchymal cells and is down regulated during valve differentiation and remodeling. Previous studies demonstrated that Twist1 promotes cell proliferation, migration, and expression of primitive extracellular matrix (ECM) molecules in ECC mesenchymal cells. Furthermore, Twist1 expression is induced in human pediatric and adult diseased heart valves. However, the Twist1 downstream target genes that mediate increased cell proliferation and migration during early heart valve development remain largely unknown. Candidate gene and global gene profiling approaches were used to identify transcriptional targets of Twist1 during heart valve development. Candidate target genes were analyzed for evolutionarily conserved regions (ECRs) containing E-box consensus sequences that are potential Twist1 binding sites. ECRs containing conserved E-box sequences were identified for Twist1 responsive genes Tbx20, Cdh11, Sema3C, Rab39b, and Gadd45a. Twist1 binding to these sequences in vivo was determined by chromatin immunoprecipitation (ChIP) assays, and binding was detected in ECCs but not late stage remodeling valves. In addition identified Twist1 target genes are highly expressed in ECCs and have reduced expression during heart valve remodeling in vivo, which is consistent with the expression pattern of Twist1. Together these analyses identify multiple new genes involved in cell proliferation and migration that are differentially expressed in the developing heart valves, are responsive to Twist1 transcriptional function, and contain Twist1-responsive regulatory sequences

The United States of America and Scientific Research

To gauge the current commitment to scientific research in the United States of America (US), we compared federal research funding (FRF) with the US gross domestic product (GDP) and industry research spending during the past six decades. In order to address the recent globalization of scientific research, we also focused on four key indicators of research activities: research and development (R&D) funding, total science and engineering doctoral degrees, patents, and scientific publications. We compared these indicators across three major population and economic regions: the US, the European Union (EU) and the People's Republic of China (China) over the past decade. We discovered a number of interesting trends with direct relevance for science policy. The level of US FRF has varied between 0.2% and 0.6% of the GDP during the last six decades. Since the 1960s, the US FRF contribution has fallen from twice that of industrial research funding to roughly equal. Also, in the last two decades, the portion of the US government R&D spending devoted to research has increased. Although well below the US and the EU in overall funding, the current growth rate for R&D funding in China greatly exceeds that of both. Finally, the EU currently produces more science and engineering doctoral graduates and scientific publications than the US in absolute terms, but not per capita. This study's aim is to facilitate a serious discussion of key questions by the research community and federal policy makers. In particular, our results raise two questions with respect to: a) the increasing globalization of science: “What role is the US playing now, and what role will it play in the future of international science?”; and b) the ability to produce beneficial innovations for society: “How will the US continue to foster its strengths?