198 research outputs found

    Adversarial training for tabular data with attack propagation

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    Adversarial attacks are a major concern in security-centered applications, where malicious actors continuously try to mislead Machine Learning (ML) models into wrongly classifying fraudulent activity as legitimate, whereas system maintainers try to stop them. Adversarially training ML models that are robust against such attacks can prevent business losses and reduce the work load of system maintainers. In such applications data is often tabular and the space available for attackers to manipulate undergoes complex feature engineering transformations, to provide useful signals for model training, to a space attackers cannot access. Thus, we propose a new form of adversarial training where attacks are propagated between the two spaces in the training loop. We then test this method empirically on a real world dataset in the domain of credit card fraud detection. We show that our method can prevent about 30% performance drops under moderate attacks and is essential under very aggressive attacks, with a trade-off loss in performance under no attacks smaller than 7%

    Global Impact of the COVID-19 Pandemic on Stroke Volumes and Cerebrovascular Events: One-Year Follow-up.

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    BACKGROUND AND OBJECTIVES Declines in stroke admission, intravenous thrombolysis, and mechanical thrombectomy volumes were reported during the first wave of the COVID-19 pandemic. There is a paucity of data on the longer-term effect of the pandemic on stroke volumes over the course of a year and through the second wave of the pandemic. We sought to measure the impact of the COVID-19 pandemic on the volumes of stroke admissions, intracranial hemorrhage (ICH), intravenous thrombolysis (IVT), and mechanical thrombectomy over a one-year period at the onset of the pandemic (March 1, 2020, to February 28, 2021) compared with the immediately preceding year (March 1, 2019, to February 29, 2020). METHODS We conducted a longitudinal retrospective study across 6 continents, 56 countries, and 275 stroke centers. We collected volume data for COVID-19 admissions and 4 stroke metrics: ischemic stroke admissions, ICH admissions, intravenous thrombolysis treatments, and mechanical thrombectomy procedures. Diagnoses were identified by their ICD-10 codes or classifications in stroke databases. RESULTS There were 148,895 stroke admissions in the one-year immediately before compared to 138,453 admissions during the one-year pandemic, representing a 7% decline (95% confidence interval [95% CI 7.1, 6.9]; p<0.0001). ICH volumes declined from 29,585 to 28,156 (4.8%, [5.1, 4.6]; p<0.0001) and IVT volume from 24,584 to 23,077 (6.1%, [6.4, 5.8]; p<0.0001). Larger declines were observed at high volume compared to low volume centers (all p<0.0001). There was no significant change in mechanical thrombectomy volumes (0.7%, [0.6,0.9]; p=0.49). Stroke was diagnosed in 1.3% [1.31,1.38] of 406,792 COVID-19 hospitalizations. SARS-CoV-2 infection was present in 2.9% ([2.82,2.97], 5,656/195,539) of all stroke hospitalizations. DISCUSSION There was a global decline and shift to lower volume centers of stroke admission volumes, ICH volumes, and IVT volumes during the 1st year of the COVID-19 pandemic compared to the prior year. Mechanical thrombectomy volumes were preserved. These results suggest preservation in the stroke care of higher severity of disease through the first pandemic year. TRIAL REGISTRATION INFORMATION This study is registered under NCT04934020

    Common femtoscopic hadron-emission source in pp collisions at the LHC

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    International audienceThe femtoscopic study of pairs of identical pions is particularly suited to investigate the effective source function of particle emission, due to the resulting Bose-Einstein correlation signal. In small collision systems at the LHC, pp in particular, the majority of the pions are produced in resonance decays, which significantly affect the profile and size of the source. In this work, we explicitly model this effect in order to extract the primordial source in pp collisions at s=13\sqrt{s} = 13 TeV from charged π\pi-π\pi correlations measured by ALICE. We demonstrate that the assumption of a Gaussian primordial source is compatible with the data and that the effective source, resulting from modifications due to resonances, is approximately exponential, as found in previous measurements at the LHC. The universality of hadron emission in pp collisions is further investigated by applying the same methodology to characterize the primordial source of K-p pairs. The size of the primordial source is evaluated as a function of the transverse mass (mTm_{\rm T}) of the pairs, leading to the observation of a common scaling for both π\pi-π\pi and K-p, suggesting a collective effect. Further, the present results are compatible with the mTm_{\rm T} scaling of the p-p and pΛ-\Lambda primordial source measured by ALICE in high multiplicity pp collisions, providing compelling evidence for the presence of a common emission source for all hadrons in small collision systems at the LHC. This will allow the determination of the source function for any hadron--hadron pairs with high precision, granting access to the properties of the possible final-state interaction among pairs of less abundantly produced hadrons, such as strange or charmed particles

    Measurement of the production cross section of prompt Ξ0c baryons in p–Pb collisions at √sNN = 5.02 TeV

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    The transverse momentum (pT) differential production cross section of the promptly-produced charm-strange baryon Ξ0c (and its charge conjugate Ξ0c¯¯¯¯¯¯) is measured at midrapidity via its hadronic decay into π+Ξ− in p−Pb collisions at a centre-of-mass energy per nucleon−nucleon collision sNN−−−√ = 5.02 TeV with the ALICE detector at the LHC. The Ξ0c nuclear modification factor (RpPb), calculated from the cross sections in pp and p−Pb collisions, is presented and compared with the RpPb of Λ+c baryons. The ratios between the pT-differential production cross section of Ξ0c baryons and those of D0 mesons and Λ+c baryons are also reported and compared with results at forward and backward rapidity from the LHCb Collaboration. The measurements of the production cross section of prompt Ξ0c baryons are compared with a model based on perturbative QCD calculations of charm-quark production cross sections, which includes only cold nuclear matter effects in p−Pb collisions, and underestimates the measurement by a factor of about 50. This discrepancy is reduced when the data is compared with a model in which hadronisation is implemented via quark coalescence. The pT-integrated cross section of prompt Ξ0c-baryon production at midrapidity extrapolated down to pT = 0 is also reported. These measurements offer insights and constraints for theoretical calculations of the hadronisation process. Additionally, they provide inputs for the calculation of the charm production cross section in p−Pb collisions at midrapidity

    Measurement of Ω0c baryon production and branching-fraction ratio BR(Ω0c → Ω−e+νe)/BR(Ω0c → Ω−π+) in pp collisions at √s = 13 TeV

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    The inclusive production of the charm-strange baryon Ω0c is measured for the first time via its semileptonic decay into Ω−e+νe at midrapidity (|y| < 0.8) in proton–proton (pp) collisions at the centre-of-mass energy √s = 13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2 < pT < 12 GeV/c. The branching-fraction ratio BR(Ω0c → Ω−e+νe)/BR(Ω0c → Ω−π+) is measured to be 1.12 ± 0.22 (stat.) ± 0.27 (syst.). Comparisons with other experimental measurements, as well as with theoretical calculations, are presented

    J/ψ\psi-hadron correlations at midrapidity in pp collisions at s\sqrt{s} = 13 TeV

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    International audienceWe report on the measurement of inclusive, non-prompt, and prompt J/ψ\psi-hadron correlations by the ALICE Collaboration at the CERN Large Hadron Collider in pp collisions at a center-of-mass energy of 13 TeV. The correlations are studied at midrapidity (y<0.9|y| < 0.9) in the transverse momentum ranges pT<40 GeV/cp_{\rm T} < 40~\text{GeV}/c for the J/ψ\psi and 0.15<pT<100.15 < p_{\rm T} < 10 GeV/cc and η<0.9|\eta|<0.9 for the associated hadrons. The measurement is based on minimum bias and high multiplicity data samples corresponding to integrated luminosities of Lint=34 nb1L_{\text{int}} = 34~\text{nb}^{-1} and Lint=6.9 pb1L_{\text{int}} = 6.9~\text{pb}^{-1}, respectively. In addition, two more data samples are employed, requiring, on top of the minimum bias condition, a threshold on the tower energy of E=4E = 4 and 9 GeV9~\text{GeV} in the ALICE electromagnetic calorimeters, which correspond to integrated luminosities of Lint=0.9 pb1L_{\text{int}} = 0.9~\text{pb}^{-1} and Lint=8.4 pb1L_{\text{int}} = 8.4~\text{pb}^{-1}, respectively. The results are presented as associated hadron yields per J/ψ\psi trigger as a function of the azimuthal angle difference between the associated hadrons and J/ψ\psi mesons. The integrated near-side and away-side correlated yields are also extracted as a function of the J/ψ\psi transverse momentum. The measurements are discussed in comparison to PYTHIA calculations

    Charm fragmentation fractions and cc{\rm c\overline{c}} cross section in p-Pb collisions at sNN=5.02\sqrt{s_{\rm NN}}=5.02 TeV

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    International audienceThe total charm-quark production cross section per unit of rapidity dσ(cc)/dy\mathrm{d}\sigma({\rm c\overline{c}})/\mathrm{d}y, and the fragmentation fractions of charm quarks to different charm-hadron species f(chc)f(\mathrm{c}\rightarrow {\rm h_{c}}), are measured for the first time in p-Pb collisions at sNN=5.02\sqrt{s_\mathrm{NN}} = 5.02 TeV at midrapidity (0.96<y<0.04-0.96<y<0.04 in the centre-of-mass frame) using data collected by ALICE at the CERN LHC. The results are obtained based on all the available measurements of prompt production of ground-state charm-hadron species: D0\mathrm{D}^{0}, D+\mathrm{D}^{+}, Ds+\mathrm{D}_\mathrm{s}^{+}, and J/ψ\mathrm{J/\psi} mesons, and Λc+\Lambda_\mathrm{c}^{+} and Ξc0\Xi_{\rm c}^{0} baryons. The resulting cross section is dσ(cc)/dy=219.6±6.3  (stat.)  11.8+10.5  (syst.)  2.9+7.6  (extr.)±5.4  (BR)±4.6  (lumi.)±19.5  (rapidity shape)+15.0  (Ωc0)\mathrm{d}\sigma({\rm c\overline{c}})/\mathrm{d}y =219.6 \pm 6.3\;(\mathrm{stat.}) {\;}_{-11.8}^{+10.5}\;(\mathrm{syst.}) {\;}_{-2.9}^{+7.6}\;(\mathrm{extr.})\pm 5.4\;(\mathrm{BR})\pm 4.6\;(\mathrm{lumi.}) \pm 19.5\;(\text{rapidity shape})+15.0\;(\Omega_{\rm c}^{0}) mb, which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are compatible with those measured in pp collisions at s=5.02\sqrt{s} = 5.02 and 1313 TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and p-Pb collisions compared with e+e\mathrm{e^{+}e^{-}} and ep\mathrm{e^{-}p} collisions. The pTp_\mathrm{T}-integrated nuclear modification factor of charm quarks, RpPb(cc)=0.91±0.04  (stat.)0.09+0.08  (syst.)0.03+0.04  (extr.)±0.03  (lumi.)R_\mathrm{pPb}({\rm c\overline{c}})= 0.91 \pm 0.04\;{\rm (stat.)}{}^{+0.08}_{-0.09}\;{\rm (syst.)}{}^{+0.04}_{-0.03}\;{\rm (extr.)}{}\pm 0.03\;{\rm (lumi.)}, is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions

    Studying the interaction between charm and light-flavor mesons

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    International audienceThe two-particle momentum correlation functions between charm mesons (D±\mathrm{D^{*\pm}} and D±\mathrm{D}^\pm) and charged light-flavor mesons (π±\pi^{\pm} and K±^{\pm}) in all charge-combinations are measured for the first time by the ALICE Collaboration in high-multiplicity proton-proton collisions at a center-of-mass energy of s=13\sqrt{s} =13 TeV. For DK\mathrm{DK} and DK\mathrm{D^*K} pairs, the experimental results are in agreement with theoretical predictions of the residual strong interaction based on quantum chromodynamics calculations on the lattice and chiral effective field theory. In the case of Dπ\mathrm{D}\pi and Dπ\mathrm{D^*}\pi pairs, tension between the calculations including strong interactions and the measurement is observed. For all particle pairs, the data can be adequately described by Coulomb interaction only, indicating a shallow interaction between charm and light-flavor mesons. Finally, the scattering lengths governing the residual strong interaction of the Dπ\mathrm{D}\pi and Dπ\mathrm{D^*}\pi systems are determined by fitting the experimental correlation functions with a model that employs a Gaussian potential. The extracted values are small and compatible with zero
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