RESUMEN
It has been conjectured that transport in integrable one-dimensional systems is necessarily ballistic. The large diffusive response seen experimentally in nearly ideal realizations of the S=1/2 1D Heisenberg model is therefore puzzling and has not been explained so far. Here, we show that, contrary to common belief, diffusion is universally present in interacting 1D systems subject to a periodic lattice potential. We present a parameter-free formula for the spin-lattice relaxation rate which is in excellent agreement with experiment. Furthermore, we calculate the current decay directly in the thermodynamic limit using a time-dependent density matrix renormalization group algorithm and show that an anomalously large time scale exists even at high temperatures.
RESUMEN
The psychological effects of false-positive mammography were evaluated in 124 women who had taken part in the U.K. National Health Service Breast Screening Programme. In addition, the effects of recall on women with and without a family history were compared. These women were asked to complete the Hospital Anxiety and Depression Scale (HADS) before being invited to attend for screening, at recall and 5 weeks and 4 months after recall. At screening and at recall, the women were asked to complete the Health Questionnaire (HQ) which measures stress-related behaviour changes in the previous week. In the week before screening, compared with women who did not have a family history of breast cancer, women with a family history had lower scores on HADS depression and reported fewer stress-related behaviour changes. At recall, regardless of family history, the women were more likely to have borderline or clinically significant anxiety than at baseline or screening. Nevertheless, for most women, recall-induced anxiety was relatively transient (less than 5 weeks). Compared with women without a family history, women with a family history were more anxious 4 months after recall, although their anxiety scores tended to be lower (P < 0.06) than at baseline. A strength of the present study is that the initial baseline measure was uncontaminated by the screening process. Women who did not complete questionnaires at one or more of the subsequent time points scored higher on HADS depression at baseline, indicating that the results are likely to have underestimated the effects of recall. Screening appears to be less stressful for women with a family history than for those without a history. However, for both groups recall causes short term distress. Breast screening programmes should ensure that steps are taken to minimise the number of women who are recalled for unnecessary investigations.