468 research outputs found
Toward Understanding Massive Star Formation
Although fundamental for astrophysics, the processes that produce massive
stars are not well understood. Large distances, high extinction, and short
timescales of critical evolutionary phases make observations of these processes
challenging. Lacking good observational guidance, theoretical models have
remained controversial. This review offers a basic description of the collapse
of a massive molecular core and a critical discussion of the three competing
concepts of massive star formation:
- monolithic collapse in isolated cores
- competitive accretion in a protocluster environment
- stellar collisions and mergers in very dense systems
We also review the observed outflows, multiplicity, and clustering properties
of massive stars, the upper initial mass function and the upper mass limit. We
conclude that high-mass star formation is not merely a scaled-up version of
low-mass star formation with higher accretion rates, but partly a mechanism of
its own, primarily owing to the role of stellar mass and radiation pressure in
controlling the dynamics.Comment: 139 pages, 18 figures, 5 tables, glossar
An unusual presentation of adenoid cystic carcinoma of the minor salivary glands with cranial nerve palsy: a case study
<p>Abstract</p> <p>Background</p> <p>Adenoid Cystic Carcinoma (ACC) is a rare tumor entity and comprises about 1% of all malignant tumor of the oral and maxillofacial region. It is slow growing but a highly invasive cancer with a high recurrence rate. Intracranial ACC is even more infrequent and could be primary or secondary occurring either by direct invasion, hematogenous spread, or perineural spread. We report the first case of the 5<sup>th </sup>and 6<sup>th </sup>nerve palsy due to cavernous sinus invasion by adenoid cystic carcinoma.</p> <p>Case presentation</p> <p>A 49-year-old African American female presented to the emergency room complaining of severe right-sided headache, photophobia, dizziness and nausea, with diplopia. The patient had a 14 year history migraine headaches, hypertension, and mild intermittent asthma. Physical examination revealed right lateral rectus muscle palsy with esotropia. There was numbness in all three divisions of the right trigeminal nerve. Motor and sensory examination of extremities was normal. An MRI of the brain/brain stem was obtained which showed a large mass in the clivus extending to involve the nasopharynx, pterygoid plate, sphenoid and right cavernous sinuses.</p> <p>Biopsy showed an ACC tumor with a cribriform pattern of the minor salivary glands. The patient underwent total gross surgical resection and radiation therapy.</p> <p>Conclusion</p> <p>This is a case of ACC of the minor salivary glands with intracranial invasion. The patient had long history of headaches which changed in character during the past year, and symptoms of acute 5<sup>th </sup>and 6<sup>th </sup>cranial nerve involvement. Our unique case demonstrates direct invasion of cavernous sinus and could explain the 5<sup>th </sup>and 6<sup>th </sup>cranial nerve involvement as histopathology revealed no perineural invasion.</p
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
A pilot study on peritraumatic dissociation and coping styles as risk factors for posttraumatic stress, anxiety and depression in parents after their child's unexpected admission to a Pediatric Intensive Care Unit
Aim: To study the prevalence of posttraumatic stress disorder (PTSD), anxiety and depression in parents three months after pediatric intensive care treatment of their child and examine if peritraumatic dissocation and coping styles are related to these mental health problems. Methods: This is a prospective cohort study and included parents of children unexpectedly admitted to the Pediatric Intensive Care Unit (PICU) from January 2006 to March 2007. At three months follow-up parents completed PTSD (n = 115), anxiety and depression (n = 128) questionnaires. Immediately after discharge, parents completed peritraumatic dissocation and coping questionnaires. Linear regression models with generalized estimating equations examined risk factors for mental health problems. Results: Over 10% of the parents were likely to meet criteria for PTSD and almost one quarter for subclinical PTSD. Respectively 15% to 23% of the parents reported clinically significant levels of depression and anxiety. Peritraumatic dissocation was most strongly associated with PTSD, anxiety as well as depression. Avoidance coping was primarily associated with PTSD. Conclusion: A significant number of parents have mental health problems three months after unexpected PICU treatment of their child. Improving detection and raise awareness of mental health problems is important to minimize the negative effect of these problems on parents' well-being. © 2009 Bronner et al; licensee BioMed Central Ltd
A monolithic integrated photonic microwave filter
[EN] Meeting the increasing demand for capacity in wireless networks requires the harnessing of higher regions in the radiofrequency spectrum, reducing cell size, as well as more compact, agile and power-efficient base stations that are capable of smoothly interfacing the radio and fibre segments. Fully functional microwave photonic chips are promising candidates in attempts to meet these goals. In recent years, many integrated microwave photonic chips have been reported in different technologies. To the best of our knowledge, none has monolithically integrated all the main active and passive optoelectronic components. Here, we report the first demonstration of a tunable microwave photonics filter that is monolithically integrated into an indium phosphide chip. The reconfigurable radiofrequency photonic filter includes all the necessary elements (for example, lasers, modulators and photodetectors), and its response can be tuned by means of control electric currents. This is an important step in demonstrating the feasibility of integrated and programmable microwave photonic processors.The authors acknowledge financial support from the Spanish Centro para el Desarrollo Tecnologico Industrial (CDTI) through the NEOTEC start-up programme, the European Commission through the 7th Research Framework Programme project, Photonic Advanced Research and Development for Integrated Generic Manufacturing (FP7-PARADIGM), the Generalitat Valenciana through the Programa para grupos de Investigacion de Excelencia (PROMETEO) project code 2013/012, the Spanish Ministerio de Economia y Comercio (MINECO) via project TEC2013-42332-P, PIF4ESP, and the Unwersitat Politecnica de Valencia (UPVOV) through projects 10-3E-492 and 08-3E-008 funded by the Fondos Europeos de Desarrollo Regional (FEDER). J.S. Fandino acknowledges financial support from Formacion de Profesorado Universitario (FPU) grant AP2010-1595.Sanchez Fandiño, JA.; Muñoz Muñoz, P.; DomĂ©nech GĂłmez, JD.; Capmany Francoy, J. (2017). A monolithic integrated photonic microwave filter. Nature Photonics. 11(2):124-129. https://doi.org/10.1038/NPHOTON.2016.233S124129112Novak, D. et al. Radio-over-fiber technologies for emerging wireless systems. IEEE J. Quantum Electron. 52, 1â11 (2016).Waterhouse, R. & Novak, D. Realizing 5G: microwave photonics for 5G mobile wireless systems. IEEE Microw. Mag. 16, 84â92 (2015).Won, R. Microwave photonics shines. Nat. Photon. 5, 736 (2011).Capmany, J. & Novak, D. Microwave photonics combines two worlds. Nat. Photon. 1, 319â330 (2007).Yao, J. Microwave photonics. J. Lightw. Technol. 27, 314â335 (2009).Andrews, J. G. et al. What will 5G be? IEEE J. Sel. Areas Commun. 32, 1065â1082 (2014).Gosh, A., et al. Millimetre-wave enhanced local area systems: a high-data-rate approach for future wireless networks. IEEE J. Sel. Areas Commun. 32, 1152â1163 (2014).Marpaung, D. et al. Integrated microwave photonics. Laser Photon. Rev. 7, 506â538 (2013).Iezekiel, S., Burla, M., Klamkin, J., Marpaung, D. & Capmany, J. RF engineering meets optoelectronics: progress in integrated microwave photonics. IEEE Microw. Mag. 16, 28â45 (2015).Mitchell, J. E. Integrated wireless backhaul over optical access networks. J. Lightw. Technol. 32, 3373â3382 (2014).Liu, C., Wang, J., Cheng, L., Zhu, M. & Chang, G.-K. Key microwave-photonics technologies for next-generation cloud-based radio access networks. J. Lightw. Technol. 32, 3452â3460 (2014).Norberg, E. J., Guzzon, R. S., Parker, J. S., Johansson, L. A. & Coldren, L. A. Programmable photonic microwave filters monolithically integrated in InP/InGaAsP. J. Lightw. Technol. 29, 1611â1619 (2011).Guzzon, R., Norberg, E., Parker, J., Johansson, L. & Coldren, L. Integrated InPâInGaAsP tuneable coupled ring optical bandpass filters with zero insertion loss. Opt. Express 19, 7816â7826 (2011).Fandiño, J. S. & Muñoz, P. Photonics-based microwave frequency measurement using a double-sideband suppressed-carrier modulation and an InP integrated ring-assisted MachâZehnder interferometer filter. Opt. Lett. 38, 4316â4319 (2013).Burla, M. et al. On-chip ultra-wideband microwave photonic phase shifter and true time delay line based on a single phase-shifted waveguide Bragg grating. In IEEE International Topical Meeting on Microwave Photonics 92â95 (IEEE, 2013).Shi, W., Veerasubramanian, V., Patel, D. & Plant, D. Tuneable nanophotonic delay lines using linearly chirped contradirectioinal couplers with uniform Bragg gratings. Opt. Lett. 39, 701â703 (2014).Guan, B. et al. CMOS compatible reconfigurable silicon photonic lattice filters using cascaded unit cells for RF-photonic processing. IEEE J. Sel. Top. Quantum Electron. 20, 359â368 (2014).Khan, M. H. et al. Ultrabroad-bandwidth arbitrary radiofrequency waveform generation with a silicon photonic chip-based spectral shaper. Nat. Photon. 4, 117â122 (2010).Pagani, M. et al. Instantaneous frequency measurement system using four-wave mixing in an ultra-compact long silicon waveguide. In Proc. 41st European Conf. on Optical Communication (ECOC) 1â3 (IEEE, 2015).Khilo, A. et al. Photonic ADC: overcoming the bottleneck of electronic jitter. Opt. Express 20, 4454â4469 (2012).Wang, J. et al. Reconfigurable radio-frequency arbitrary waveforms synthesized in a silicon photonic chip. Nat. Commun. 6, 5957 (2015).Marpaung, D. et al. Si3N4 ring resonator-based microwave photonic notch filter with an ultrahigh peak rejection. Opt. Express 21, 23286â23294 (2013).Zhuang, L. et al. Ring resonator-based on-chip modulation transformer for high-performance phase-modulated microwave photonic links. Opt. Express 21, 25999â26013 (2013).Marpaung, D., Chevalier, L., Burla, M. & Roeloffzen, C. Impulse radio ultrawideband pulse shaper based on a programmable photonic chip frequency discriminator. Opt. Express 19, 24838â24848 (2011).Marpaung, D. On-chip photonic-assisted instantaneous microwave frequency measurement system. IEEE Photon. Technol. Lett. 25, 837â840 (2013).Burla, M. et al. On-chip CMOS compatible reconfigurable optical delay line with separate carrier tuning for microwave photonic signal processing. Opt. Express 19, 21475â21484 (2011).Tan, K. et al. Photonic-chip-based all-optical ultra-wideband pulse generation via XPM and birefringence in a chalcogenide waveguide. Opt. Express 21, 2003â2011 (2013).Pagani, M. et al. Tuneable wideband microwave photonic phase shifter using on-chip stimulated Brillouin scattering. Opt. Express 22, 28810â28818 (2014).PĂ©rez, D., Gasulla, I. & Capmany, J. Software-defined reconfigurable microwave photonics processor. Opt. Express 23, 14640â14654 (2015).Capmany, J., Gasulla, I. & PĂ©rez, D. Microwave photonics: the programmable processor. Nat. Photon. 10, 6â8 (2016).Zhuang, L., Roeloffzen, C. G. H., Hoekman, M., Boller, K.-J. & Lowery, A. J. Programmable photonic signal processor chip for radiofrequency applications. Optica 2, 854â859 (2015).Roeloffzen, C. G. et al. Silicon nitride microwave photonic circuits. Opt. Express 21, 22937â22961 (2013).Liu, W. et al. A fully reconfigurable photonic integrated signal processor. Nat. Photon. 10, 190â195 (2016).Madsen, C. K. & Zhao, J. H. Optical Filter Design and Analysis: A Signal Processing Approach (Wiley, 1999).RomĂĄn, J., Frankel, M. Y. & Esman, R. D. Spectral characterization of fiber gratings with high resolution. Opt. Lett. 23, 939â941 (1998).HernĂĄndez, R., Loayssa, A. & Benito, D. Optical vector network analysis based on single-sideband modulation. Opt. Eng. 43, 2418â2421 (2004).Jinguji, K. & Oguma, M. Optical half-band filters. J. Lightw. Technol. 18, 252â259 (2000).Madsen, C. K. Efficient architectures for exactly realizing optical filters with optimum bandpass designs. IEEE Photon. Technol. Lett. 10, 1136â1138 (1998).Madsen, C. K. General IIR optical filter design for WDM applications using all-pass filters. J. Lightw. Technol. 18, 860â868 (2000).Smit, M. K. et al. An introduction to InP-based generic integration technology. Semicond. Sci. Technol. 29, 083001 (2014).Besse, P. A., Gini, E., Bachmann, M. & Melchior, H. New 2Ă2 and 1Ă3 multimode interference couplers with free selection of power splitting ratios. J. Lightw. Technol. 14, 2286â2293 (1996).PĂ©rez, D. et al. Figures of merit for self-beating filtered microwave photonic systems. Opt. Express 24, 10087â10102 (2016).Zhuang, L. et al. Novel low-loss waveguide delay lines using Vernier ring resonators for on-chip multi-λ microwave photonic signal processors. Laser Photon. Rev. 7, 994â1002 (2013)
Measurement of the cross-section of high transverse momentum vector bosons reconstructed as single jets and studies of jet substructure in pp collisions at âs = 7 TeV with the ATLAS detector
This paper presents a measurement of the cross-section for high transverse momentum W and Z bosons produced in pp collisions and decaying to all-hadronic final states. The data used in the analysis were recorded by the ATLAS detector at the CERN Large Hadron Collider at a centre-of-mass energy of âs = 7 TeV;{\rm Te}{\rm V}4.6\;{\rm f}{{{\rm b}}^{-1}}{{p}_{{\rm T}}}\gt 320\;{\rm Ge}{\rm V}|\eta |\lt 1.9{{\sigma }_{W+Z}}=8.5\pm 1.7$ pb and is compared to next-to-leading-order calculations. The selected events are further used to study jet grooming techniques
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
Search for the neutral Higgs bosons of the minimal supersymmetric standard model in pp collisions at root s=7 TeV with the ATLAS detector
A search for neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is based on a sample of proton-proton collisions at a centre-of-mass energy of 7TeV recorded with the ATLAS detector at the Large Hadron Collider. The data were recorded in 2011 and correspond to an integrated luminosity of 4.7 fb-1 to 4.8 fb-1. Higgs boson decays into oppositely-charged muon or Ï lepton pairs are considered for final states requiring either the presence or absence of b-jets. No statistically significant excess over the expected background is observed and exclusion limits at the 95% confidence level are derived. The exclusion limits are for the production cross-section of a generic neutral Higgs boson, Ï, as a function of the Higgs boson mass and for h/A/H production in the MSSM as a function of the parameters mA and tan ÎČ in the mhmax scenario for mA in the range of 90GeV to 500 GeV. Copyright CERN
Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at sâ=8 TeV with the ATLAS detector
The results of a search for direct pair production of the scalar partner to the top quark using an integrated luminosity of 20.1fbâ1 of protonâproton collision data at âs = 8 TeV recorded with the ATLAS detector at the LHC are reported. The top squark is assumed to decay via tËâtÏË01 or tËâ bÏ˱1 âbW(â)ÏË01 , where ÏË01 (Ï˱1 ) denotes the lightest neutralino (chargino) in supersymmetric models. The search targets a fully-hadronic final state in events with four or more jets and large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits are reported in terms of the top squark and neutralino masses and as a function of the branching fraction of tË â tÏË01 . For a branching fraction of 100%, top squark masses in the range 270â645 GeV are excluded for ÏË01 masses below 30 GeV. For a branching fraction of 50% to either tË â tÏË01 or tË â bÏ˱1 , and assuming the Ï˱1 mass to be twice the ÏË01 mass, top squark masses in the range 250â550 GeV are excluded for ÏË01 masses below 60 GeV
Search for R-parity-violating supersymmetry in events with four or more leptons in sqrt(s) =7 TeV pp collisions with the ATLAS detector
A search for new phenomena in final states with four or more leptons (electrons or muons) is presented. The analysis is based on 4.7 fbâ1 of proton-proton collisions delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in two signal regions: one that requires moderate values of missing transverse momentum and another that requires large effective mass. The results are interpreted in a simplified model of R-parity-violating supersymmetry in which a 95% CL exclusion region is set for charged wino masses up to 540 GeV. In an R-parity-violating MSUGRA/CMSSM model, values of m 1/2 up to 820 GeV are excluded for 10 < tan ÎČ < 40
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