Electron-phonon coupling and spin-charge separation in one-dimensional Mott insulators

We examine the single-particle excitation spectrum in the one-dimensional Hubbard-Holstein model at half-filling by performing the dynamical density matrix renormalization group (DDMRG) calculation. The DDMRG results are interpreted as superposition of spectra for a spinless carrier dressed with phonons. The superposition is a consequence of robustness of the spin-charge separation against electron-phonon coupling. The separation is in contrast to the coupling between phonon and spin degrees of freedom in two-dimensional systems. We discuss implication of the results of the recent angle-resolved photoemission spectroscopy measurements on SrCuO${}_{2}$.Comment: 5 pages, 4 figures. submitted to the Physical Review Letter

Polaron in t-J model

We present numeric results for ground state and angle resolved photoemission spectra (ARPES) for single hole in t-J model coupled to optical phonons. The systematic-error free diagrammatic Monte Carlo is employed where the Feynman graphs for the Matsubara Green function in imaginary time are summed up completely with respect to phonons variables, while magnetic variables are subjected to non-crossing approximation. We obtain that at electron-phonon coupling constants relevant for high Tc cuprates the polaron undergoes self-trapping crossover to strong coupling limit and theoretical ARPES demonstrate features observed in experiment: a broad peak in the bottom of the spectra has momentum dependence which coincides with that of hole in pure t-J model.Comment: 4 pages, 4 figure

Maternal posttraumatic stress disorder during the perinatal period and child outcomes: A systematic review

BACKGROUND: Approximately 3.3% of women in pregnancy have posttraumatic stress disorder (PTSD) and 4% of women postpartum PTSD. The impact of maternal PTSD during the perinatal period (from conception until one year postpartum) on child outcomes has not been systematically examined. METHOD: A systematic review was conducted to synthesize and critically evaluate quantitative research investigating the association between perinatal PTSD and child outcomes. Databases EMBASE, BNI, Medline, PsycInfo and CINAHL were searched using specific inclusion and exclusion criteria. RESULTS: 26 papers reporting 21 studies were identified that examined associations between perinatal PTSD and postpartum birth outcomes, child development, and mother-infant relationship. Studies reviewed were heterogeneous, with poor-to-medium scores of methodological quality. Results showed that maternal postpartum PTSD is associated with low birth weight and lower rates of breastfeeding. Evidence for an association between maternal PTSD and preterm birth, fetal growth, head circumference, mother-infant interaction, the mother-infant relationship or child development is contradictory. Associations between maternal PTSD and infant salivary cortisol levels, and eating/sleeping difficulties are based on single studies, so require replication. LIMITATIONS: Methodological weaknesses of the studies included insufficient sample size, use of invalidated measures, and limited external validity. CONCLUSION: Findings suggest that perinatal PTSD is linked with some negative child outcomes. Early screening for PTSD during the perinatal period may be advisable and onward referral for effective treatment, if appropriate. Future research using larger sample sizes, validated and reliable clinical interviews to assess PTSD, and validated measures to assess a range of child outcomes, is needed

Acute and Post-traumatic Stress Disorder Symptoms in Mothers and Fathers Following Childbirth: A Prospective Cohort Study.

Introduction: Up to 30% of women view their childbirth as traumatic. This experience can lead to acute stress disorder or post-traumatic stress disorder. The negative impact of maternal post-traumatic stress disorder following childbirth reaches beyond the mother, potentially affecting her child's development and the couple's relationship. Research on paternal post-traumatic stress disorder following childbirth is scarce. Acute stress disorder is suggested to be an important predictor of post-traumatic stress disorder in mothers, but little is known about paternal acute stress disorder following childbirth. Furthermore, there is limited information about the comparison or relation of acute stress disorder and post-traumatic stress disorder following childbirth between parents. Aim: [1] To compare the prevalence rates and severity of acute stress disorder and post-traumatic stress disorder symptoms between parents following childbirth by taking anxiety and depression symptoms, as well as obstetric variables and previous traumatic events into account and [2] To determine if acute stress disorder is a predictor of post-traumatic stress disorder. Method: A prospective population-based design was used. N = 647 participants were recruited from future parents who attended appointments at the Obstetrics and Gynecology unit at a Swiss university hospital. Self-report questionnaires were used: Post-traumatic Diagnostic Scale in the third trimester of pregnancy (T1) and 1 month post-partum (T3), Acute Stress Disorder Scale at 1 week post-partum (T2), and Hospital Anxiety and Depression Scale at all time points. Obstetric and neonatal variables were retrieved from hospital records. Results: At T2, 63.9% of mothers and 51.7% of fathers presented symptoms of acute stress disorder. At T3, 20.7% of mothers and 7.2% of fathers had symptoms of post-traumatic stress disorder. Acute stress disorder was a predictor of post-partum post-traumatic stress disorder (Odds ratio: 8.6, IC 95% [1.85; 40.42]). Depression symptoms was a significant confounder in the prediction of post-traumatic stress disorder following childbirth, but not anxiety or previous perinatal loss. Conclusion: Little is known about parental differences in acute stress disorder and post-traumatic stress disorder symptoms following childbirth. Results indicate that both parents may suffer from acute stress disorder and post-traumatic stress disorder symptoms after childbirth and that acute stress disorder is a predictor of post-traumatic stress disorder after childbirth for both parents. Sensitization of maternity staff to these results may assist in earlier identification of and appropriate treatment for at-risk parents

Anomalous bond stretching phonons as a probe of charge fluctuations in perovskites

Important information on momentum resolved low energy charge response can be extracted from anomalous properties of bond stretching in plane phonons observed in inelastic neutron and X-ray scattering in cuprates and some other perovskites. We discuss a semiphenomenological model based on coupling of phonons to a single charge mode. The phonon dispersion and linewidth allow to locate the energy of the charge excitation in the mid infrared part of the spectrum and to determine some of its characteristics. New experiments on oxygen isotope substitution could allow to achieve a more detailed description. Corresponding relations following from the model can be used for the interpretation of experiments and as test of the model.Comment: presented at the M2S-HTSC-VIII conference in Dresde

Investigating prenatal perceived support as protective factor against adverse birth outcomes: a community cohort study.

Studies show that prenatal maternal anxiety may act as a risk factor for adverse birth outcomes, whilst prenatal social support may rather act as a protective factor. However, studies examining prenatal anxiety symptoms, prenatal perceived support, and neonatal and/or obstetric outcomes are lacking. This study investigated whether, in a community sample, prenatal perceived support: (1) had a protective influence on birth outcomes (gestational age (GA), birthweight (BW), 5-minute Apgar score, and mode of delivery); (2) acted as a protective factor, moderating the relationship between anxiety symptoms and the aforementioned birth outcomes. During their third trimester of pregnancy, 182 nulliparous child-bearers completed standardized questionnaires of anxiety (HADS-A) and perceived support (MOS-SSS). Birth outcomes data was extracted from medical records. (1) Perceived support did not significantly predict any birth outcomes. However, perceived tangible support - MOS-SSS subscale assessing perceived material/financial aid - significantly positively predicted the 5-minute Apgar score. (2) Perceived support did not significantly moderate the relationship between anxiety symptoms and birth outcomes. However, perceived tangible support significantly moderated the relationship between anxiety symptoms and the 5-minute Apgar score. When experienced within non-clinical thresholds, prenatal anxiety symptoms do not increase the risk of adverse neonatal and obstetric outcomes when perceived support is present

Numerical renormalization group study of the correlation functions of the antiferromagnetic spin-12\frac{1}{2} Heisenberg chain

We use the density-matrix renormalization group technique developed by White \cite{white} to calculate the spin correlation functions $=(-1)^l \omega(l,N)$ for isotropic Heisenberg rings up to $N=70$ sites. The correlation functions for large $l$ and $N$ are found to obey the scaling relation $\omega(l,N)=\omega(l,\infty)f_{XY}^{\alpha} (l/N)$ proposed by Kaplan et al. \cite{horsch} , which is used to determine $\omega(l,\infty)$. The asymptotic correlation function $\omega(l,\infty)$ and the magnetic structure factor $S(q=\pi)$ show logarithmic corrections consistent with $\omega(l,\infty)\sim a\sqrt{\ln{cl}}/l$, where $c$ is related to the cut-off dependent coupling constant $g_{eff}(l_0)=1/\ln(cl_0)$, as predicted by field theoretical treatments.Comment: Accepted in Phys. Rev. B. 4 pages of text in Latex + 5 figures in uuencoded form containing the 5 postscripts (mailed separately