Bound states for massive Dirac fermions in graphene in a magnetic step field

We calculate the spectrum of massive Dirac fermions in graphene in the presence of an inhomogeneous magnetic field modeled by a step function. We find an analytical universal relation between the bandwidths and the propagating velocities of the modes at the border of the magnetic region, showing how by tuning the mass term one can control the speed of these traveling edge states.Comment: 7 pages, 3 figure

Modeling the Temporal Nature of Human Behavior for Demographics Prediction

Mobile phone metadata is increasingly used for humanitarian purposes in developing countries as traditional data is scarce. Basic demographic information is however often absent from mobile phone datasets, limiting the operational impact of the datasets. For these reasons, there has been a growing interest in predicting demographic information from mobile phone metadata. Previous work focused on creating increasingly advanced features to be modeled with standard machine learning algorithms. We here instead model the raw mobile phone metadata directly using deep learning, exploiting the temporal nature of the patterns in the data. From high-level assumptions we design a data representation and convolutional network architecture for modeling patterns within a week. We then examine three strategies for aggregating patterns across weeks and show that our method reaches state-of-the-art accuracy on both age and gender prediction using only the temporal modality in mobile metadata. We finally validate our method on low activity users and evaluate the modeling assumptions.Comment: Accepted at ECML 2017. A previous version of this paper was titled 'Using Deep Learning to Predict Demographics from Mobile Phone Metadata' and was accepted at the ICLR 2016 worksho

Improving official statistics in emerging markets using machine learning and mobile phone data

Mobile phones are one of the fastest growing technologies in the developing world with global penetration rates reaching 90%. Mobile phone data, also called CDR, are generated everytime phones are used and recorded by carriers at scale. CDR have generated groundbreaking insights in public health, official statistics, and logistics. However, the fact that most phones in developing countries are prepaid means that the data lacks key information about the user, including gender and other demographic variables. This precludes numerous uses of this data in social science and development economic research. It furthermore severely prevents the development of humanitarian applications such as the use of mobile phone data to target aid towards the most vulnerable groups during crisis. We developed a framework to extract more than 1400 features from standard mobile phone data and used them to predict useful individual characteristics and group estimates. We here present a systematic cross-country study of the applicability of machine learning for dataset augmentation at low cost. We validate our framework by showing how it can be used to reliably predict gender and other information for more than half a million people in two countries. We show how standard machine learning algorithms trained on only 10,000 users are sufficient to predict individual’s gender with an accuracy ranging from 74.3 to 88.4% in a developed country and from 74.5 to 79.7% in a developing country using only metadata. This is significantly higher than previous approaches and, once calibrated, gives highly accurate estimates of gender balance in groups. Performance suffers only marginally if we reduce the training size to 5,000, but significantly decreases in a smaller training set. We finally show that our indicators capture a large range of behavioral traits using factor analysis and that the framework can be used to predict other indicators of vulnerability such as age or socio-economic status. Mobile phone data has a great potential for good and our framework allows this data to be augmented with vulnerability and other information at a fraction of the cost

Experimental study of subwavelength grating bimodal waveguides as ultrasensitive interferometric sensors

[EN] Over the recent years, subwavelength grating (SWG) structures have increasingly attracted attention in the area of evanescent-field photonic sensors. In this Letter, for the first time to the best of our knowledge, we demonstrate experimentally the real-time refractive index (RI) sensing using the SWG bimodal interferometric structures. Two different configurations are considered to compare the effect of the nonlinear phase shift, obtained between the two first transverse electromagnetic propagating modes, in the measured bulk sensitivity. Very high experimental values up to 2270 nm/RIU are reached, which perfectly match the numerical simulations and significantly enhance other existing SWG and spectralbased sensors. By measuring the spectral shift, the obtained experimental sensitivity does not depend on the sensor length. As a result, a highly sensitive and compact singlechannel interferometer is experimentally validated for refractive index sensing, thus opening new paths in the field of optical integrated sensors.European Commission (PHC-634013 PHOCNOSIS project); Spanish Government (TEC2015-63838-C3-1-R-OPTONANOSENS project); Universitat Politecnica de Valencia (grant PAID 01-18).Torrijos-Morán, L.; Griol Barres, A.; García-Rupérez, J. (2019). Experimental study of subwavelength grating bimodal waveguides as ultrasensitive interferometric sensors. Optics Letters. 44(19):4702-4705. https://doi.org/10.1364/OL.44.004702S470247054419Cheben, P., Xu, D.-X., Janz, S., & Densmore, A. (2006). Subwavelength waveguide grating for mode conversion and light coupling in integrated optics. Optics Express, 14(11), 4695. doi:10.1364/oe.14.004695Schmid, J. H., Cheben, P., Janz, S., Lapointe, J., Post, E., & Xu, D.-X. (2007). Gradient-index antireflective subwavelength structures for planar waveguide facets. Optics Letters, 32(13), 1794. doi:10.1364/ol.32.001794Bock, P. J., Cheben, P., Schmid, J. H., Lapointe, J., Delâge, A., Janz, S., … Hall, T. J. (2010). Subwavelength grating periodic structures in silicon-on-insulator: a new type of microphotonic waveguide. Optics Express, 18(19), 20251. doi:10.1364/oe.18.020251Halir, R., Bock, P. J., Cheben, P., Ortega‐Moñux, A., Alonso‐Ramos, C., Schmid, J. H., … Janz, S. (2014). Waveguide sub‐wavelength structures: a review of principles and applications. Laser & Photonics Reviews, 9(1), 25-49. doi:10.1002/lpor.201400083Cheben, P., Halir, R., Schmid, J. H., Atwater, H. A., & Smith, D. R. (2018). Subwavelength integrated photonics. Nature, 560(7720), 565-572. doi:10.1038/s41586-018-0421-7Gonzalo Wangüemert-Pérez, J., Cheben, P., Ortega-Moñux, A., Alonso-Ramos, C., Pérez-Galacho, D., Halir, R., … Schmid, J. H. (2014). Evanescent field waveguide sensing with subwavelength grating structures in silicon-on-insulator. Optics Letters, 39(15), 4442. doi:10.1364/ol.39.004442Donzella, V., Sherwali, A., Flueckiger, J., Grist, S. M., Fard, S. T., & Chrostowski, L. (2015). Design and fabrication of SOI micro-ring resonators based on sub-wavelength grating waveguides. Optics Express, 23(4), 4791. doi:10.1364/oe.23.004791Flueckiger, J., Schmidt, S., Donzella, V., Sherwali, A., Ratner, D. M., Chrostowski, L., & Cheung, K. C. (2016). Sub-wavelength grating for enhanced ring resonator biosensor. Optics Express, 24(14), 15672. doi:10.1364/oe.24.015672Yan, H., Huang, L., Xu, X., Chakravarty, S., Tang, N., Tian, H., & Chen, R. T. (2016). Unique surface sensing property and enhanced sensitivity in microring resonator biosensors based on subwavelength grating waveguides. Optics Express, 24(26), 29724. doi:10.1364/oe.24.029724Huang, L., Yan, H., Xu, X., Chakravarty, S., Tang, N., Tian, H., & Chen, R. T. (2017). Improving the detection limit for on-chip photonic sensors based on subwavelength grating racetrack resonators. Optics Express, 25(9), 10527. doi:10.1364/oe.25.010527Benedikovic, D., Berciano, M., Alonso-Ramos, C., Le Roux, X., Cassan, E., Marris-Morini, D., & Vivien, L. (2017). Dispersion control of silicon nanophotonic waveguides using sub-wavelength grating metamaterials in near- and mid-IR wavelengths. Optics Express, 25(16), 19468. doi:10.1364/oe.25.019468Halir, R., Cheben, P., Luque‐González, J. M., Sarmiento‐Merenguel, J. D., Schmid, J. H., Wangüemert‐Pérez, G., … Molina‐Fernández, Í. (2016). Ultra‐broadband nanophotonic beamsplitter using an anisotropic sub‐wavelength metamaterial. Laser & Photonics Reviews, 10(6), 1039-1046. doi:10.1002/lpor.201600213Luque-González, J. M., Herrero-Bermello, A., Ortega-Moñux, A., Molina-Fernández, Í., Velasco, A. V., Cheben, P., … Halir, R. (2018). Tilted subwavelength gratings: controlling anisotropy in metamaterial nanophotonic waveguides. Optics Letters, 43(19), 4691. doi:10.1364/ol.43.004691Jahani, S., Kim, S., Atkinson, J., Wirth, J. C., Kalhor, F., Noman, A. A., … Jacob, Z. (2018). Controlling evanescent waves using silicon photonic all-dielectric metamaterials for dense integration. Nature Communications, 9(1). doi:10.1038/s41467-018-04276-8Torrijos-Morán, L., & García-Rupérez, J. (2019). Single-channel bimodal interferometric sensor using subwavelength structures. Optics Express, 27(6), 8168. doi:10.1364/oe.27.008168Levy, R., & Ruschin, S. (2009). Design of a Single-Channel Modal Interferometer Waveguide Sensor. IEEE Sensors Journal, 9(2), 146-1. doi:10.1109/jsen.2008.2011075Zinoviev, K. E., Gonzalez-Guerrero, A. B., Dominguez, C., & Lechuga, L. M. (2011). Integrated Bimodal Waveguide Interferometric Biosensor for Label-Free Analysis. Journal of Lightwave Technology, 29(13), 1926-1930. doi:10.1109/jlt.2011.2150734Kozma, P., Kehl, F., Ehrentreich-Förster, E., Stamm, C., & Bier, F. F. (2014). Integrated planar optical waveguide interferometer biosensors: A comparative review. Biosensors and Bioelectronics, 58, 287-307. doi:10.1016/j.bios.2014.02.049Levy, R., & Ruschin, S. (2008). Critical sensitivity in hetero-modal interferometric sensor using spectral interrogation. Optics Express, 16(25), 20516. doi:10.1364/oe.16.020516García-Rupérez, J., Toccafondo, V., Bañuls, M. J., Castelló, J. G., Griol, A., Peransi-Llopis, S., & Maquieira, Á. (2010). Label-free antibody detection using band edge fringes in SOI planar photonic crystal waveguides in the slow-light regime. Optics Express, 18(23), 24276. doi:10.1364/oe.18.024276Zhang, W., Serna, S., Le Roux, X., Vivien, L., & Cassan, E. (2016). Highly sensitive refractive index sensing by fast detuning the critical coupling condition of slot waveguide ring resonators. Optics Letters, 41(3), 532. doi:10.1364/ol.41.000532Di Falco, A., O’Faolain, L., & Krauss, T. F. (2009). Chemical sensing in slotted photonic crystal heterostructure cavities. Applied Physics Letters, 94(6), 063503. doi:10.1063/1.3079671Molina-Fernández, Í., Leuermann, J., Ortega-Moñux, A., Wangüemert-Pérez, J. G., & Halir, R. (2019). Fundamental limit of detection of photonic biosensors with coherent phase read-out. Optics Express, 27(9), 12616. doi:10.1364/oe.27.01261

Directed self-assembly of a helical nanofilament liquid crystal phase for use as structural color reflectors

The fabrication of molecular structures with a desired morphology, e.g., nanotubes, nanoribbons, nanosprings, and sponges, is essential for the advancement of nanotechnology. Unfortunately, realization of this objective is expensive and complicated. Here, we report that irradiating a film comprising azobenzene derivatives with UV light produces oriented arrays of helical nanofilaments via the photoisomerization-induced Weigert effect. As a result, structural colors are observed due to the extrinsic chiral reflection in the visible wavelength range, and the reflected color can be tuned by adjusting the molecular length of the azobenzene derivative. This simple fabrication method can be used for fabricating large, reversible, and patternable color reflectors, providing a new platform for interference-based structural coloration as it exists in nature, such as morpho butterflies, green-winged teal, and various beetles

Prevalence and Correlates of Hepatitis C Infection among Male Injection Drug Users in Detention, Tehran, Iran

For the benefit of planning for the future care and treatment of people infected with hepatitis C virus (HCV) and to help guide prevention and control programs, data are needed on HCV seroprevalence and associated risk factors. We conducted a cross-sectional sero-behavioral survey of injection drug users (IDU) detained for mandatory rehabilitation during a police sweep of Tehran, Iran, in early 2006. During the study period, a consecutive sample comprising 454 of 499 (91.0%) men arrested and determined to be IDU by urine test and physical examination consented to a face-to-face interview and blood collection for HCV antibody testing. Overall, HCV prevalence was 80.0% (95% confidence interval (CI) 76.2–83.6). Factors independently associated with HCV infection included history of incarceration (adjusted OR 4.35, 95% CI 1.88–10.08), age of first injection ≤25 years (OR 2.72, 95% CI 1.09–6.82), and history of tattooing (OR 2.33, 95% CI 1.05–5.17). HCV prevalence in this population of IDU upon intake to jail was extremely high and possibly approaching saturation. Findings support that incarceration is contributing to the increased spread of HCV infection in Iran and calls for urgent increased availability of HCV treatment, long-term preparation for the care of complications of chronic infection, and rapid scale-up of programs for the primary prevention of parenterally transmitted infections among drug users

Glutamate Induces Mitochondrial Dynamic Imbalance and Autophagy Activation: Preventive Effects of Selenium

Glutamate-induced cytotoxicity is partially mediated by enhanced oxidative stress. The objectives of the present study are to determine the effects of glutamate on mitochondrial membrane potential, oxygen consumption, mitochondrial dynamics and autophagy regulating factors and to explore the protective effects of selenium against glutamate cytotoxicity in murine neuronal HT22 cells. Our results demonstrated that glutamate resulted in cell death in a dose-dependent manner and supplementation of 100 nM sodium selenite prevented the detrimental effects of glutamate on cell survival. The glutamate induced cytotoxicity was associated with mitochondrial hyperpolarization, increased ROS production and enhanced oxygen consumption. Selenium reversed these alterations. Furthermore, glutamate increased the levels of mitochondrial fission protein markers pDrp1 and Fis1 and caused increase in mitochondrial fragmentation. Selenium corrected the glutamate-caused mitochondrial dynamic imbalance and reduced the number of cells with fragmented mitochondria. Finally, glutamate activated autophagy markers Beclin 1 and LC3-II, while selenium prevented the activation. These results suggest that glutamate targets the mitochondria and selenium supplementation within physiological concentration is capable of preventing the detrimental effects of glutamate on the mitochondria. Therefore, adequate selenium supplementation may be an efficient strategy to prevent the detrimental glutamate toxicity and further studies are warranted to define the therapeutic potentials of selenium in animal disease models and in human

A TNF-JNK-Axl-ERK signaling axis mediates primary resistance to EGFR inhibition in glioblastoma.

Aberrant epidermal growth factor receptor (EGFR) signaling is widespread in cancer, making the EGFR an important target for therapy. EGFR gene amplification and mutation are common in glioblastoma (GBM), but EGFR inhibition has not been effective in treating this tumor. Here we propose that primary resistance to EGFR inhibition in glioma cells results from a rapid compensatory response to EGFR inhibition that mediates cell survival. We show that in glioma cells expressing either EGFR wild type or the mutant EGFRvIII, EGFR inhibition triggers a rapid adaptive response driven by increased tumor necrosis factor (TNF) secretion, which leads to activation in turn of c-Jun N-terminal kinase (JNK), the Axl receptor tyrosine kinase and extracellular signal-regulated kinases (ERK). Inhibition of this adaptive axis at multiple nodes rendered glioma cells with primary resistance sensitive to EGFR inhibition. Our findings provide a possible explanation for the failures of anti-EGFR therapy in GBM and suggest a new approach to the treatment of EGFR-expressing GBM using a combination of EGFR and TNF inhibition