Chiral tunneling and the Klein paradox in graphene

The so-called Klein paradox - unimpeded penetration of relativistic particles through high and wide potential barriers - is one of the most exotic and counterintuitive consequences of quantum electrodynamics (QED). The phenomenon is discussed in many contexts in particle, nuclear and astro- physics but direct tests of the Klein paradox using elementary particles have so far proved impossible. Here we show that the effect can be tested in a conceptually simple condensed-matter experiment by using electrostatic barriers in single- and bi-layer graphene. Due to the chiral nature of their quasiparticles, quantum tunneling in these materials becomes highly anisotropic, qualitatively different from the case of normal, nonrelativistic electrons. Massless Dirac fermions in graphene allow a close realization of Klein's gedanken experiment whereas massive chiral fermions in bilayer graphene offer an interesting complementary system that elucidates the basic physics involved.Comment: 15 pages, 4 figure

Boundary Terms and Junction Conditions for Generalized Scalar-Tensor Theories

We compute the boundary terms and junction conditions for Horndeski's panoptic class of scalar-tensor theories, and write the bulk and boundary equations of motion in explicitly second order form. We consider a number of special subclasses, including galileon theories, and present the corresponding formulae. Our analysis opens up of the possibility of studying tunnelling between vacua in generalized scalar-tensor theories, and braneworld dynamics. The latter follows because our results are independent of spacetime dimension.Comment: 13 pages, Equation corrected. Thanks to Tsutomu Kobayashi for informing us of the typ

Absence of association between behavior problems in childhood and hypertension in midlife

Background It is known that behavior in childhood is associated with certain physical and mental health problems in midlife. However, there is limited evidence on the role of childhood behavior problems in the development of hypertension in adulthood. The present study aimed to examine whether behavior problems in childhood influenced the risk of hypertension in midlife in the United Kingdom 1958 birth cohort. Methods The 1958 British birth cohort comprised 17,638 individuals born in the first week of March 1958 in the United Kingdom. Behavior problems were assessed at 7, 11, and 16 years of age by parents and teachers. At age 45, blood pressure was measured and hypertension was recorded if blood pressure was ≥140/90 mm Hg or if the participants were informed by their health professionals that they had high blood pressure. Behavioral information was reported according to the Rutter Children's Behaviour Questionnaire (RCBQ) and the Bristol Social Adjustment Guide (BSAG). Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to examine behavior problems in childhood in relation to hypertension at 45 years of age according to logistic regression analysis, with adjustment for sex, social class in childhood and adulthood, childhood cognition, birth weight, gestational age at birth, body mass index (BMI), smoking, alcohol consumption, and physical activity. Results Behavior problems reported by parents at 7, 11, and 16 years were not associated with hypertension in midlife (OR, 0.93; 95% CI, 0.81, 1.07; OR, 0.95; 95% CI, 0.81, 1.11; OR, 0.98; 95% CI, 0.85, 1.12, respectively). Similarly, teacher-reported behavior problems at 7, 11, and 16 years were not associated with hypertension in midlife (OR, 0.92; 95% CI, 0.72, 1.18; OR, 0.92; 95% CI, 0.84, 1.02; OR, 1.03; 95% CI, 0.92, 1.15, respectively). Further separate analyses showed similar results for males and females. Conclusion There is no association between behavior problems in childhood and hypertension in midlife

Higher Dimensional Cylindrical or Kasner Type Electrovacuum Solutions

We consider a D dimensional Kasner type diagonal spacetime where metric functions depend only on a single coordinate and electromagnetic field shares the symmetries of spacetime. These solutions can describe static cylindrical or cosmological Einstein-Maxwell vacuum spacetimes. We mainly focus on electrovacuum solutions and four different types of solutions are obtained in which one of them has no four dimensional counterpart. We also consider the properties of the general solution corresponding to the exterior field of a charged line mass and discuss its several properties. Although it resembles the same form with four dimensional one, there is a difference on the range of the solutions for fixed signs of the parameters. General magnetic field vacuum solution are also briefly discussed, which reduces to Bonnor-Melvin magnetic universe for a special choice of the parameters. The Kasner forms of the general solution are also presented for the cylindrical or cosmological cases.Comment: 16 pages, Revtex. Text and references are extended, Published versio

Simultaneous Effects of Light Intensity and Phosphorus Supply on the Sterol Content of Phytoplankton

Sterol profiles of microalgae and their change with environmental conditions are of great interest in ecological food web research and taxonomic studies alike. Here, we investigated effects of light intensity and phosphorus supply on the sterol content of phytoplankton and assessed potential interactive effects of these important environmental factors on the sterol composition of algae. We identified sterol contents of four common phytoplankton genera, Scenedesmus, Chlamydomonas, Cryptomonas and Cyclotella, and analysed the change in sterol content with varying light intensities in both a high-phosphorus and a low-phosphorus approach. Sterol contents increased significantly with increasing light in three out of four species. Phosphorus-limitation reversed the change of sterol content with light intensity, i.e., sterol content decreased with increasing light at low phosphorus supply. Generally sterol contents were lower in low-phosphorus cultures. In conclusion, both light and phosphorus conditions strongly affect the sterol composition of algae and hence should be considered in ecological and taxonomic studies investigating the biochemical composition of algae. Data suggest a possible sterol limitation of growth and reproduction of herbivorous crustacean zooplankton during summer when high light intensities and low phosphorus supply decrease sterol contents of algae

Pro- and antisaccades in children elicited by visual and acoustic targets - does modality matter?

Peer reviewedPublisher PD

Resurrecting melancholia

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65798/1/j.1600-0447.2007.00958.x.pd

Stationary Black Holes: Uniqueness and Beyond

The spectrum of known black-hole solutions to the stationary Einstein equations has been steadily increasing, sometimes in unexpected ways. In particular, it has turned out that not all black-hole-equilibrium configurations are characterized by their mass, angular momentum and global charges. Moreover, the high degree of symmetry displayed by vacuum and electro-vacuum black-hole spacetimes ceases to exist in self-gravitating non-linear field theories. This text aims to review some developments in the subject and to discuss them in light of the uniqueness theorem for the Einstein-Maxwell system.Comment: Major update of the original version by Markus Heusler from 1998. Piotr T. Chru\'sciel and Jo\~ao Lopes Costa succeeded to this review's authorship. Significantly restructured and updated all sections; changes are too numerous to be usefully described here. The number of references increased from 186 to 32

Optical Cloaking with Non-Magnetic Metamaterials

Artificially structured metamaterials have enabled unprecedented flexibility in manipulating electromagnetic waves and producing new functionalities, including the cloak of invisibility based on coordinate transformation. Here we present the design of a non-magnetic cloak operating at optical frequencies. The principle and structure of the proposed cylindrical cloak are analyzed, and the general recipe for the implementation of such a device is provided. The cloaking performance is verified using full-wave finite-element simulations.Comment: 10 pages, 4 figure