Efficient metallic spintronic emitters of ultrabroadband terahertz radiation

Terahertz electromagnetic radiation is extremely useful for numerous applications such as imaging and spectroscopy. Therefore, it is highly desirable to have an efficient table-top emitter covering the 1-to-30-THz window whilst being driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source which relies on tailored fundamental spintronic and photonic phenomena in magnetic metal multilayers: ultrafast photo-induced spin currents, the inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an analytical model, such spintronic route offers unique possibilities for systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer generates ultrashort pulses fully covering the 1-to-30-THz range. Our novel source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals in terms of bandwidth, terahertz-field amplitude, flexibility, scalability and cost.Comment: 18 pages, 10 figure

Large-scale Nonlinear Variable Selection via Kernel Random Features

We propose a new method for input variable selection in nonlinear regression. The method is embedded into a kernel regression machine that can model general nonlinear functions, not being a priori limited to additive models. This is the first kernel-based variable selection method applicable to large datasets. It sidesteps the typical poor scaling properties of kernel methods by mapping the inputs into a relatively low-dimensional space of random features. The algorithm discovers the variables relevant for the regression task together with learning the prediction model through learning the appropriate nonlinear random feature maps. We demonstrate the outstanding performance of our method on a set of large-scale synthetic and real datasets.Comment: Final version for proceedings of ECML/PKDD 201

Secondary organic aerosol production from diesel vehicle exhaust: impact of aftertreatment, fuel chemistry and driving cycle

Environmental chamber ("smog chamber") experiments were conducted to investigate secondary organic aerosol (SOA) production from dilute emissions from two medium-duty diesel vehicles (MDDVs) and three heavy-duty diesel vehicles (HDDVs) under urban-like conditions. Some of the vehicles were equipped with emission control aftertreatment devices, including diesel particulate filters (DPFs), selective catalytic reduction (SCR) and diesel oxidation catalysts (DOCs). Experiments were also performed with different fuels (100% biodiesel and low-, medium- or high-aromatic ultralow sulfur diesel) and driving cycles (Unified Cycle,~Urban Dynamometer Driving Schedule, and creep + idle). During normal operation, vehicles with a catalyzed DPF emitted very little primary particulate matter (PM). Furthermore, photooxidation of dilute emissions from these vehicles produced essentially no SOA (below detection limit). However, significant primary PM emissions and SOA production were measured during active DPF regeneration experiments. Nevertheless, under reasonable assumptions about DPF regeneration frequency, the contribution of regeneration emissions to the total vehicle emissions is negligible, reducing PM trapping efficiency by less than 2%. Therefore, catalyzed DPFs appear to be very effective in reducing both primary PM emissions and SOA production from diesel vehicles. For both MDDVs and HDDVs without aftertreatment substantial SOA formed in the smog chamber – with the emissions from some vehicles generating twice as much SOA as primary organic aerosol after 3 h of oxidation at typical urban VOC / NO_x ratios (3 : 1). Comprehensive organic gas speciation was performed on these emissions, but less than half of the measured SOA could be explained by traditional (speciated) SOA precursors. The remainder presumably originates from the large fraction (~30%) of the nonmethane organic gas emissions that could not be speciated using traditional one-dimensional gas chromatography. The unspeciated organics – likely comprising less volatile species such as intermediate volatility organic compounds – appear to be important SOA precursors; we estimate that the effective SOA yield (defined as the ratio of SOA mass to reacted precursor mass) was 9 ± 6% if both speciated SOA precursors and unspeciated organics are included in the analysis. SOA production from creep + idle operation was 3–4 times larger than SOA production from the same vehicle operated over the Urban Dynamometer Driving Schedule (UDDS). Fuel properties had little or no effect on primary PM emissions or SOA formation

Effects Of Length, Complexity, And Grammatical Correctness On Stuttering In Spanish-Speaking Preschool Children

Purpose: To explore the effects of utterance length, syntactic complexity, and grammatical correctness on stuttering in the spontaneous speech of young, monolingual Spanish-speaking children. Method: Spontaneous speech samples of 11 monolingual Spanish-speaking children who stuttered, ages 35 to 70 months, were examined. Mean number of syllables, total number of clauses, utterance complexity (i.e., containing no clauses, simple clauses, or subordinate and/or conjoined clauses), and grammatical correctness (i.e., the presence or absence of morphological and syntactical errors) in stuttered and fluent utterances were compared. Results: Findings revealed that stuttered utterances in Spanish tended to be longer and more often grammatically incorrect, and contain more clauses, including more subordinate and/or conjoined clauses. However, when controlling for the interrelatedness of syllable number and clause number and complexity, only utterance length and grammatical incorrectness were significant predictors of stuttering in the spontaneous speech of these Spanish-speaking children. Use of complex utterances did not appear to contribute to the prediction of stuttering when controlling for utterance length. Conclusions: Results from the present study were consistent with many earlier reports of English-speaking children. Both length and grammatical factors appear to affect stuttering in Spanish-speaking children. Grammatical errors, however, served as the greatest predictor of stuttering.Communication Sciences and Disorder

The GAPS Programme with HARPS-N@TNG VI: The Curious Case of TrES-4b

We revisit the TrES-4 system parameters based on high-precision HARPS-N radial-velocity measurements and new photometric light curves. A combined spectroscopic and photometric analysis allows us to determine a spectroscopic orbit with an amplitude $K=51\pm3$ m s$^{-1}$. The derived mass of TrES-4b is found to be $M_{\rm p} = 0.49\pm0.04 \rm M_{Jup}$, significantly lower than previously reported. Combined with the large radius ($R_{\rm p} = 1.84_{-0.09}^{+0.08} \rm R_{Jup}$) inferred from our analysis, TrES-4b becomes the second-lowest density transiting hot Jupiter known. We discuss several scenarios to explain the puzzling discrepancy in the mass of TrES-4b in the context of the exotic class of highly inflated transiting giant planets.Comment: 5 pages, 4 figures, Letter accepted for publication in Astronomy and Astrophysic

GeantV: Results from the prototype of concurrent vector particle transport simulation in HEP

Full detector simulation was among the largest CPU consumer in all CERN experiment software stacks for the first two runs of the Large Hadron Collider (LHC). In the early 2010's, the projections were that simulation demands would scale linearly with luminosity increase, compensated only partially by an increase of computing resources. The extension of fast simulation approaches to more use cases, covering a larger fraction of the simulation budget, is only part of the solution due to intrinsic precision limitations. The remainder corresponds to speeding-up the simulation software by several factors, which is out of reach using simple optimizations on the current code base. In this context, the GeantV R&D project was launched, aiming to redesign the legacy particle transport codes in order to make them benefit from fine-grained parallelism features such as vectorization, but also from increased code and data locality. This paper presents extensively the results and achievements of this R&D, as well as the conclusions and lessons learnt from the beta prototype.Comment: 34 pages, 26 figures, 24 table

First Observation of PP-odd γ\gamma Asymmetry in Polarized Neutron Capture on Hydrogen

We report the first observation of the parity-violating 2.2 MeV gamma-ray asymmetry $A^{np}_\gamma$ in neutron-proton capture using polarized cold neutrons incident on a liquid parahydrogen target at the Spallation Neutron Source at Oak Ridge National Laboratory. $A^{np}_\gamma$ isolates the $\Delta I=1$, \mbox{$^{3}S_{1}\rightarrow {^{3}P_{1}}$} component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to a single coupling constant in either the DDH meson exchange model or pionless EFT. We measured $A^{np}_\gamma = [-3.0 \pm 1.4 (stat) \pm 0.2 (sys)]\times 10^{-8}$, which implies a DDH weak $\pi NN$ coupling of $h_{\pi}^{1} = [2.6 \pm 1.2(stat) \pm 0.2(sys)] \times 10^{-7}$ and a pionless EFT constant of $C^{^{3}S_{1}\rightarrow ^{3}P_{1}}/C_{0}=[-7.4 \pm 3.5 (stat) \pm 0.5 (sys)] \times 10^{-11}$ MeV$^{-1}$. We describe the experiment, data analysis, systematic uncertainties, and the implications of the result.Comment: 6 pages, 5 figure

Multiple glass transitions in star polymer mixtures: Insights from theory and simulations

The glass transition in binary mixtures of star polymers is studied by mode coupling theory and extensive molecular dynamics computer simulations. In particular, we have explored vitrification in the parameter space of size asymmetry $\delta$ and concentration $\rho_2$ of the small star polymers at fixed concentration of the large ones. Depending on the choice of parameters, three different glassy states are identified: a single glass of big polymers at low $\delta$ and low $\rho_2$, a double glass at high $\delta$ and low $\rho_2$, and a novel double glass at high $\rho_2$ and high $\delta$ which is characterized by a strong localization of the small particles. At low $\delta$ and high $\rho_2$ there is a competition between vitrification and phase separation. Centered in the $(\delta, \rho_2)$-plane, a liquid lake shows up revealing reentrant glass formation. We compare the behavior of the dynamical density correlators with the predictions of the theory and find remarkable agreement between the two.Comment: 15 figures, to be published in Macromolecule