Perceived friend support buffers against symptoms of depression in peer victimized adolescents: Evidence from a population-based cohort in South Korea.

BACKGROUND: Peer victimization is associated with an increased risk for depression, but there is less evidence on how certain factors such as friend support can buffer this association. This study investigated the associations between friend support and depressive symptoms among victimized and non-victimized adolescent girls and boys from South Korea. METHODS: Participants includes 2258 students from the Korean Children and Youth Panel Survey, a nationally representative sample of middle school students in South Korea. Self-reported perceived friend support, depressive symptoms and peer victimization were measured using validated scales during middle school year 3 (mean age= 15.7 years). RESULTS: The association between peer victimization and depressive symptoms varied by sex (p for sex by peer victimization interaction<0.05). Peer victimization was more strongly associated with same year depressive symptoms in girls (ß=0.55) than boys (ß=0.24). After controlling for key confounders, including prior year mental health symptoms, higher levels of friend support were found to attenuate the association between peer victimization and depressive symptoms (p for friend support by peer victimization interaction <0.05). Peer victimization was associated with more depressive symptoms for adolescents with low and moderate friend support, but not those with high friend support. LIMITATIONS: Peer victimization, depressive symptoms, and friend support, were self-reported and measured the same year. CONCLUSIONS: Friend support protects victimized South Korean adolescents from the negative effect of peer victimization on depressive symptoms, hence contributes to closing the gap in depression between victimized and non-victimized adolescents.

Measurements of Nonsinglet Moments of the Nucleon Structure Functions and Comparison to Predictions from Lattice QCD for Q

We present extractions of the nucleon nonsinglet moments utilizing new precision data on the deuteron F_{2} structure function at large Bjorken-x determined via the Rosenbluth separation technique at Jefferson Lab Experimental Hall C. These new data are combined with a complementary set of data on the proton previously measured in Hall C at similar kinematics and world datasets on the proton and deuteron at lower x measured at SLAC and CERN. The new Jefferson Lab data provide coverage of the upper third of the x range, crucial for precision determination of the higher moments. In contrast to previous extractions, these moments have been corrected for nuclear effects in the deuteron using a new global fit to the deuteron and proton data. The obtained experimental moments represent an order of magnitude improvement in precision over previous extractions using high x data. Moreover, recent exciting developments in lattice QCD calculations provide a first ever comparison of these new experimental results with calculations of moments carried out at the physical pion mass, as well as a new approach that first calculates the quark distributions directly before determining moments.

Polarization components in π0 photoproduction at photon energies up to 5.6 GeV.

We present new data for the polarization observables of the final state proton in the (1)H(γ,p)π(0) reaction. These data can be used to test predictions based on hadron helicity conservation and perturbative QCD. These data have both small statistical and systematic uncertainties and were obtained with beam energies between 1.8 and 5.6 GeV and for π(0) scattering angles larger than 75° in the center-of-mass frame. The data extend the polarization measurements database for neutral pion photoproduction up to E(γ)=5.6 GeV. The results show a nonzero induced polarization above the resonance region. The polarization transfer components vary rapidly with the photon energy and π(0) scattering angle in the center-of-mass frame. This indicates that hadron helicity conservation does not hold and that the perturbative QCD limit is still not reached in the energy regime of this experiment.

Nature of the decrease of the secondary-electron yield by electron bombardment and its energy dependence.

We performed a combined secondary electron yield (SEY) and x-ray photoelectron spectroscopy study as a function of the electron dose and energy on a Cu technical surface representative of the LHC accelerator walls. The electron bombardment is accompanied by a clear chemical modification, indicating an increased graphitization as the SEY decreases. The decrease in the SEY is also found to depend significantly on the kinetic energy of the primary electrons. When low-energy primary electrons are employed (E≤20 eV), the reduction of the SEY is slower and smaller in magnitude than when higher-energy electrons are used. Consequences of this observation are discussed mainly for their relevance on the commissioning scenario for the LHC in operation at CERN (Geneva), but are expected to be of interest for other research fields.

Search for effects beyond the born approximation in polarization transfer observables in e(over→)p elastic scattering.

Intensive theoretical and experimental efforts over the past decade have aimed at explaining the discrepancy between data for the proton electric to magnetic form factor ratio, G(E)/G(M), obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange contribution. In an effort to search for effects beyond the one-photon-exchange or Born approximation, we report measurements of polarization transfer observables in the elastic H(e[over →],e(')p[over →]) reaction for three different beam energies at a Q(2)=2.5 GeV(2), spanning a wide range of the kinematic parameter ε. The ratio R, which equals µ(p)G(E)/G(M) in the Born approximation, is found to be independent of ε at the 1.5% level. The ε dependence of the longitudinal polarization transfer component P(ℓ) shows an enhancement of (2.3±0.6)% relative to the Born approximation at large ε.

Role of many body shake-up in core-valence-valence electron emission from single wall carbon nanotubes.

Auger core-valence-valence transitions from single wall Carbon nanotubes are studied using a tight-binding calculational scheme with nearest neighbor overlap, hopping interactions, and a double-zeta basis set. The resulting Hamiltonian approximates the unperturbed pi and sigma bands of the nanomaterials coupled with the free electron states outside the solid and the core-hole. As a first step, the Fermi's golden rule is applied to determine the so called one-electron spectrum of emitted electrons from different tubes, in which either the neutralizing or the ejected electrons, in the initial state, lie within nearest neighboring atomic sites to the core-hole. Many-body corrections are effectively modeled using a broadening function, which accounts for dynamic screening effects involving the initial and final states. Particular attention is paid to the asymmetric component of the broadening function, responsible for the shake-up of pi electrons. Finally, the Cini-Sawatzky distortion function is used to describe the final state effect of the hole-hole interaction. A quantitative estimation of the interplay of shake-up processes is proposed by adjusting the asymmetric parameters of the broadening function to reproduce measurements of Auger electrons ejected from bundles of single wall Carbon nanotubes.

Recoil polarization measurements of the proton electromagnetic form factor ratio to Q2 = 8.5 GeV2.

Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon's quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this Letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil polarization method, at momentum transfers Q2=5.2, 6.7, and 8.5 GeV2. By extending the range of Q2 for which G(E)(p) is accurately determined by more than 50%, these measurements will provide significant constraints on models of nucleon structure in the nonperturbative regime.

Secondary electron emission spectra from clean and cesiated Al surfaces: the role of plasmon decay and data analysis for applications.

We report measurements of energy spectra of secondary electrons emitted from clean and cesiated aluminum surfaces under the impact of 130 eV electrons. Measurements show that the decay of bulk and surface plasmons dominates the electron emission. In contrast with theoretical calculations, our experiments indicate that the electron collision cascade inside the solid produced by electrons excited by plasmon decay do not contribute significantly to electron emission. A simple analysis of electron energy distributions measured as a function of Cs surface coverage allows separation of rediffused incident electrons from the continuum background of true secondary electrons. The result shows that yields of rediffused electrons used in several applications may have been significantly overestimated.