Some comments on the divergence of perturbation series in Quantum Eletrodynamics

It has been argued by Dyson that the perturbation series in coupling constant in QED can not be convergent. We find that similiar albeit slightly different arguments lead to the divergence of the series of $1/N_f$ expansion in QED.Comment: Final Version, To appear in Modern Physics Letters

Exploration of pain in children on antiretroviral treatment in a regional hospital in South Africa

Background: Patients with human immunodeficiency virus (HIV) disease on antiretroviral therapy (ART) may experience pain for a variety of reasons, including the effects of the virus itself, associated opportunistic infections and the ART. Studies indicate that pain in adults on ART is frequent, can be severe, and is often undertreated. This study sought to explore the experience, and the prevalence of pain in young children aged 3-13 years on ART.Method: Primary caregivers of children aged 3-13 years on ART attending a paediatric ART clinic at a regional hospital in Durban participated in the study. Convenience sampling was used. The Wong-Baker FACES™ Pain Rating Scale and a questionnaire adapted from Hirshefeld were used to investigate variables such as age, cluster of differentiation 4 (CD4)count, ART regimen, ART duration, and site, prevalence and impact of pain during activities. Data were analysed using a standard statistical programme.Results: Four hundred and twenty primary caregivers were interviewed. Most were mothers caring for their HIV-positive children, and the majority of the children were aged 3-7 years. Most children were on a first-line ART regimen, and half reported pain. Nociceptive pain (visceral or somatic) was the most common type of pain, and pain interfered with the daily activities of a third of the children. There was a significant association between CD4 count and pain (p-value = 0.040). Paracetamol was the most commonly used analgesic.Conclusion: Pain was a common problem, and generally was undertreated with analgesia. A need to improve pain assessment and management in this population group was identified

Non-relativistic limit of Randall-Sundrum model: solutions, applications and constraints

In the Randall-Sundrum model with one brane, we found the approximate and exact solutions for gravitational potentials and accelerations of test bodies in these potentials for different geometrical configurations. We applied these formulas for calculation of the gravitational interaction between two spheres and found the approximate and exact expressions for the relative force corrections to the Newton's gravitational force. We demonstrated that the difference between relative force corrections for the approximate and exact cases increases with the parameter $l$ (for the fixed distance $r$ between centers of the spheres). On the other hand, this difference increases with decreasing of the distance between the centers of the spheres (for the fixed curvature scale parameter $l$). We got the upper limit for the curvature scale parameter $l\lesssim 10\, \mu$m. For these values of $l$, the difference between the approximate and exact solutions is negligible.Comment: LaTex 11 pages, 3 figure

Entropic forces generated by grafted semiflexible polymers

The entropic force exerted by the Brownian fluctuations of a grafted semiflexible polymer upon a rigid smooth wall are calculated both analytically and by Monte Carlo simulations. Such forces are thought to play an important role for several cellular phenomena, in particular, the physics of actin-polymerization-driven cell motility and movement of bacteria like Listeria. In the stiff limit, where the persistence length of the polymer is larger than its contour length, we find that the entropic force shows scaling behavior. We identify the characteristic length scales and the explicit form of the scaling functions. In certain asymptotic regimes we give simple analytical expressions which describe the full results to a very high numerical accuracy. Depending on the constraints imposed on the transverse fluctuations of the filament there are characteristic differences in the functional form of the entropic forces; in a two-dimensional geometry the entropic force exhibits a marked peak.Comment: 21 pages, 18 figures, minor misprints correcte