Three-dimensional elastostatics of a layer and a layered medium

This paper is concerned with the determination of the distribution of stresses and displacements in an infinite three-dimensional, linear, elastic, isotropic, homogeneous layer subjected to concentrated body forces acting upon an arbitrary internal point.In §2 and §3 the governing partial differential field equations are reduced to a system or ordinary differential equations by the use of the two-dimensional Fourier transform, taken with respect to the two in-plane geometric variables (§4). Analytical expressions for the stresses and displacements are then obtained for the particular case of concentrated body forces, represented as Dirac delta functions (§5).The results are subsequently utilized to formulate the multilayered medium problem by means of transfer matrices. In §8 the typical problem of a non-adhesive layered medium is undertaken.     

Spectroscopy of Ethylenedione and Ethynediolide: A Reinvestigation

In an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron‐photofragment coincidence (PPC) spectroscopy was applied to measure anions at m/z 56 and 57 using a pulsed discharge of glyoxal vapor and N₂O. PPC measurements at a photon energy of 3.20 eV yield photoelectron spectra in coincidence with either neutral photofragments or stable neutral products. The measurements showed that primarily stable neutral products were formed, with photoelectron spectra consistent with the oxyallyl diradical, C₃H₄O, and acetone enolate radical, C₃H₅O. The spectra were also found to have features nearly identical to those reported for OCCO and HOCCO by Sanov and co‐workers. The stability of the neutral products, as well as an examination of spectra reported for the oxyallyl anion and acetone enolate show that the previous assignments of OCCO and HOCCO are in error, and are instead attributed here to the oxyallyl diradical, C₃H₄O, and the acetone enolate radical, C₃H₅O.     

Discovery of novel polyamine analogs with anti-protozoal activity by computer guided drug repositioning

Chagas disease is a parasitic infection caused by the protozoa Trypanosoma cruzi that affects about 6 million people in Latin America. Despite its sanitary importance, there are currently only two drugs available for treatment: benznidazole and nifurtimox, both exhibiting serious adverse effects and limited efficacy in the chronic stage of the disease. Polyamines are ubiquitous to all living organisms where they participate in multiple basic functions such as biosynthesis of nucleic acids and proteins, proliferation and cell differentiation. T. cruzi is auxotroph for polyamines, which are taken up from the extracellular medium by efficient transporters and, to a large extent, incorporated into trypanothione (bis-glutathionylspermidine), the major redox cosubstrate of trypanosomatids. From a 268-compound database containing polyamine analogs with and without inhibitory effect on T. cruzi we have inferred classificatory models that were later applied in a virtual screening campaign to identify anti-trypanosomal compounds among drugs already used for other therapeutic indications (i.e. computer-guided drug repositioning) compiled in the DrugBank and Sweetlead databases. Five of the candidates identified with this strategy were evaluated in cellular models from different pathogenic trypanosomatids (T. cruzi wt, T. cruzi PAT12, T. brucei and Leishmania infantum), and in vitro models of aminoacid/polyamine transport assays and trypanothione synthetase inhibition assay. Triclabendazole, sertaconazole and paroxetine displayed inhibitory effects on the proliferation of T. cruzi (epimastigotes) and the uptake of putrescine by the parasite. They also interfered with the uptake of others aminoacids and the proliferation of infective T. brucei and L. infantum (promastigotes). Trypanothione synthetase was ruled out as molecular target for the anti-parasitic activity of these compounds.     

Search for ZH → l+ l- bb production in 4.2 fb(-1) of pp collisions at sqrt[s] =1 .96 TeV

We present a search for the standard model Higgs boson produced in association with a Z boson in 4.2 fb(-1) of pp collisions, collected with the D0 detector at the Fermilab Tevatron at sqrt[s] =1 .96 TeV. Selected events contain one reconstructed Z → e+ e- or Z → μ+ μ- candidate and at least two jets, including at least one b-tagged jet. In the absence of an excess over the background expected from other standard model processes, limits on the ZH cross section multiplied by the branching ratios are set. The limit at M(H) = 115 GeV is a factor of 5.9 larger than the standard model prediction.     

Observation of the Bc meson in the exclusive decay Bc-->J/psipi

A fully reconstructed Bc-->J/psipi signal is observed with the D0 detector at the Fermilab Tevatron pp[over] collider using 1.3 fb(-1) of integrated luminosity. The signal consists of 54+/-12 candidates with a significance that exceeds 5 standard deviations, and confirms earlier observations of this decay. The measured mass of the Bc meson is 6300+/-14(stat)+/-5(syst) MeV/c2.     

Observation and properties of the orbitally excited B_(s2)(*) meson

We report the direct observation of the excited L=1 state B_(s2)(*) in fully reconstructed decays to B+K-. The mass of the B_(s2)(*) meson is measured to be 5839.6+/-1.1(stat)+/-0.7(syst) MeV/c(2), and its production rate relative to the B+ meson is measured to be [1.15+/-0.23(stat)+/-0.13(syst)]%.     

Simultaneous measurement of the ratio R=B(t --> Wb)/B(t --> Wq) and the top-quark pair production cross section with the D0 detector at sqrt(s) = 1.96 TeV

We present the first simultaneous measurement of the ratio of branching fractions, R=B(t --> Wb)/B(t --> Wq), with q being a d, s, or b quark, and the top-quark pair production cross section sigma(tt[over]) in the lepton plus jets channel using 0.9 fb(-1) of pp[over] collision data at sqrt(s)=1.96 TeV collected with the D0 detector. We extract R and sigma(tt[over]) by analyzing samples of events with 0, 1, and > or =2 identified b jets. We measure R=0.97(+0.09)/(-0.08)(stat+syst) and sigma(tt[over])=8.18(+0.09)(-0.84)(stat+syst) +/- 0.50(lumi) pb, in agreement with the standard model prediction.     

Measurement of the forward-backward charge asymmetry in top-quark pair production

We present the first measurement of the integrated forward-backward charge asymmetry in top-quark-top-antiquark pair (tt) production in proton-antiproton (pp) collisions in the lepton+jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming tt + X production and decay, a sample of 0.9 fb(-1) of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on tt+X production via a Z' resonance.     

Observation of ZZ production in p-p collisions at sqrt s=1.96 TeV

We present an observation for ZZ-->l+l-l'+l'- (l, l'=e or mu) production in p[over]p collisions at a center-of-mass energy of sqrt[s]=1.96 TeV. Using 1.7 fb(-1) of data collected by the D0 experiment at the Fermilab Tevatron Collider, we observe three candidate events with an expected background of 0.14(+0.03)_(-0.02) events. The significance of this observation is 5.3 standard deviations. The combination of D0 results in this channel, as well as in ZZ-->l+l- nu[over]nu, yields a significance of 5.7 standard deviations and a combined cross section of sigma(ZZ)=1.60+/-0.63(stat)+0.16_-0.17(syst) pb.     

Search for long-lived particles decaying into electron or photon pairs with the D0 detector

In this Letter we report on a search for long-lived particles that decay into final states with two electrons or photons. Such long-lived particles arise in a variety of theoretical models, such as hidden valleys and supersymmetry with gauge-mediated breaking. By precisely reconstructing the direction of the electromagnetic shower we are able to probe much longer lifetimes than previously explored. We see no evidence of the existence of such long-lived particles and interpret this search as a quasi model-independent limit on their production cross section, as well as a limit on a long-lived fourth generation quark.