The Single-Particle Spectral Function of 16O^{16}{\rm O}

The influence of short-range correlations on the $p$-wave single-particle spectral function in $^{16}{\rm O}$ is studied as a function of energy. This influence, which is represented by the admixture of high-momentum components, is found to be small in the $p$-shell quasihole wave functions. It is therefore unlikely that studies of quasihole momentum distributions using the $(e,e'p)$ reaction will reveal a significant contribution of high momentum components. Instead, high-momentum components become increasingly more dominant at higher excitation energy. The above observations are consistent with the energy distribution of high-momentum components in nuclear matter.Comment: 5 pages, RevTeX, 3 figure

Realistic Model of the Nucleon Spectral Function in Few- and Many- Nucleon Systems

By analysing the high momentum features of the nucleon momentum distribution in light and complex nuclei, it is argued that the basic two-nucleon configurations generating the structure of the nucleon Spectral Function at high values of the nucleon momentum and removal energy, can be properly described by a factorised ansatz for the nuclear wave function, which leads to a nucleon Spectral Function in the form of a convolution integral involving the momentum distributions describing the relative and center-of-mass motion of a correlated nucleon-nucleon pair embedded in the medium. The Spectral Functions of $^3He$ and infinite nuclear matter resulting from the convolution formula and from many-body calculations are compared, and a very good agreement in a wide range of values of nucleon momentum and removal energy is found. Applications of the model to the analysis of inclusive and exclusive processes are presented, illustrating those features of the cross section which are sensitive to that part of the Spectral Function which is governed by short-range and tensor nucleon-nucleon correlations.Comment: 40 pages Latex , 16 ps figures available from the above e-mail address or from [email protected]

On the constraints violation in forward dynamics of multibody systems

It is known that the dynamic equations of motion for constrained mechanical multibody systems are frequently formulated using the Newton-Euler’s approach, which is augmented with the acceleration constraint equations. This formulation results in the establishment of a mixed set of partial differential and algebraic equations, which are solved in order to predict the dynamic behavior of general multibody systems. The classical resolution of the equations of motion is highly prone to constraints violation because the position and velocity constraint equations are not fulfilled. In this work, a general and comprehensive methodology to eliminate the constraints violation at the position and velocity levels is offered. The basic idea of the described approach is to add corrective terms to the position and velocity vectors with the intent to satisfy the corresponding kinematic constraint equations. These corrective terms are evaluated as function of the Moore-Penrose generalized inverse of the Jacobian matrix and of the kinematic constraint equations. The described methodology is embedded in the standard method to solve the equations of motion based on the technique of Lagrange multipliers. Finally, the effectiveness of the described methodology is demonstrated through the dynamic modeling and simulation of different planar and spatial multibody systems. The outcomes in terms of constraints violation at the position and velocity levels, conservation of the total energy and computational efficiency are analyzed and compared with those obtained with the standard Lagrange multipliers method, the Baumgarte stabilization method, the augmented Lagrangian formulation, the index-1 augmented Lagrangian and the coordinate partitioning method.The first author expresses his gratitude to the Portuguese Foundation for Science and Technology through the PhD grant (PD/BD/114154/2016). This work has been supported by the Portuguese Foundation for Science and Technology with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145-FEDER-006941.info:eu-repo/semantics/publishedVersio

First onset of suicidal thought and behaviors in college

Background College students are a worldwide increasing group of young people at risk for suicidal thoughts and behaviours (STB). However, no previous studies have prospectively investigated the first onset of STB during the college period. Methods Using longitudinal data from the Leuven College Surveys, 2337 (response rate [RR]=66.6%) incoming freshmen provided baseline data on STB, parental psychopathology, childhood-adolescent traumatic experiences, 12-month risk for mental disorders, and 12-month stressful experiences. A total of 1253 baseline respondents provided data on 12-month STB in a two-year annual follow-up survey (conditional RR=53.6%; college dropout adjusted conditional RR=70.2%). Results One-year incidence of first-onset STB was 4.8–6.4%. Effect sizes of the included risk factors varied considerably whether viewed from individual-level (ORs=1.91–17.58) or population-level perspective (PARPs=3.4–34.3%). Dating violence prior to the age of 17, physical abuse prior to the age of 17, and 12-month betrayal by someone else than the partner were most strong predictors for first-onset suicidal ideation (ORs=4.23–12.25; PARPs=8.7–27.1%) and plans (ORs=6.57–17.58; PARPs=15.2–34.3%). Multivariate prediction (AUC=0.84–0.91) revealed that 50.7–65.7% of first-onset STB cases were concentrated in the 10% at highest predicted risk. Limitations As this is a first investigation of STB onset in college, future studies should use validation samples to test the accuracy of our multivariate prediction model. Conclusions The first onset of STB in college appears to be higher than in the general population. Screening at college entrance is a promising strategy to identify those students at highest prospective risk, enabling the cost-efficient clinical assessment of young adults in college