The Cosmological Constant

This is a review of the physics and cosmology of the cosmological constant. Focusing on recent developments, I present a pedagogical overview of cosmology in the presence of a cosmological constant, observational constraints on its magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity (http://www.livingreviews.org/), December 199

Toward a Comprehensive Approach to the Collection and Analysis of Pica Substances, with Emphasis on Geophagic Materials

Pica, the craving and subsequent consumption of non-food substances such as earth, charcoal, and raw starch, has been an enigma for more than 2000 years. Currently, there are little available data for testing major hypotheses about pica because of methodological limitations and lack of attention to the problem.In this paper we critically review procedures and guidelines for interviews and sample collection that are appropriate for a wide variety of pica substances. In addition, we outline methodologies for the physical, mineralogical, and chemical characterization of these substances, with particular focus on geophagic soils and clays. Many of these methods are standard procedures in anthropological, soil, or nutritional sciences, but have rarely or never been applied to the study of pica.Physical properties of geophagic materials including color, particle size distribution, consistency and dispersion/flocculation (coagulation) should be assessed by appropriate methods. Quantitative mineralogical analyses by X-ray diffraction should be made on bulk material as well as on separated clay fractions, and the various clay minerals should be characterized by a variety of supplementary tests. Concentrations of minerals should be determined using X-ray fluorescence for non-food substances and inductively coupled plasma-atomic emission spectroscopy for food-like substances. pH, salt content, cation exchange capacity, organic carbon content and labile forms of iron oxide should also be determined. Finally, analyses relating to biological interactions are recommended, including determination of the bioavailability of nutrients and other bioactive components from pica substances, as well as their detoxification capacities and parasitological profiles.This is the first review of appropriate methodologies for the study of human pica. The comprehensive and multi-disciplinary approach to the collection and analysis of pica substances detailed here is a necessary preliminary step to understanding the nutritional enigma of non-food consumption

Dynamic function after anterior cruciate ligament ~ . reconstruction with autologous patellar tendon

ABSTRACT The purpose of this study was to dynamically assess the functional outcome of patients who had undergone successful anterior cruciate ligament reconstruction using an autologous patellar tendon technique and to determine whether their dynamic knee function was related to quadriceps and hamstring muscle strength. The knee kinematics and kinetics of 22 subjects who had undergone anterior cruciate ligament reconstruction (mean age, 27 Ϯ 11 years) and of 22 age-and sex-matched healthy control subjects were determined during various dynamic activities using a computerized motion analysis and force plate system. The differences in the sagittal plane angles and external moments between the two groups during light (walking), moderate (climbing and descending stairs), and higher-demand (jogging, jog and cut, jog and stop) activities were related to isokinetic strength measurements. Although patients who are asymptomatic and functioning well after anterior cruciate ligament reconstruction can perform normally in light activities, higher-demand activities reveal persistent functional adaptations that require further study. Injury to the ACL leads to knee instability and functional adaptations. Although many ACL-deficient patients display little or no visible impairment (primarily because of activity modification), previous studies have shown that patients with ACL deficiencies walk and perform more stressful activities differently than do uninjured subjects, with most of the differences occurring in the sagittal plane angles and moments. The purpose of our study was to determine whether functional adaptations during gait and other low-and high-demand activities were present in patients with an ACL bone-patellar tendon reconstruction and, if so, whether they were related to strength. More specifically, we examined how the sagittal plane joint angles and external moments during walking, stair-climbing, and jogging activities differed between healthy subjects and patients with a reconstructed ACL and whether those differences related to isokinetic quadriceps and hamstring muscle strength. MATERIALS AND METHODS Twenty-two subjects (mean age, 27 Ϯ 11 years) who underwent an autogenous patellar tendon reconstruction for ACL deficiency were tested and compared with a group of 22 uninjured control subjects. The ACL-reconstructed group consisted of 13 men and 9 women. Patients in the ACL-reconstructed group underwent surgery at an average of 8 months (range, 1 to 24) after injury and were examined at a mean follow-up of 22 Ϯ 12 months. Excluded from the study were those patients who had meniscal damage in which more than 25% of the meniscus was removed, posterior cruciate or collateral ligament injury, articular surface injury, symptomatic anterior knee pain, or objective instability at latest follow-up examination (positive pivot shift test results, positive Lachman † Address correspondence and reprint requests to Charles A. Bush-Joseph, MD, Rush-Presbyterian-St

The development of milliKelvin Si bolometers for future X-ray array devices

Silicon bolometers are currently under development for milliKelvin operation; these devices are being produced using Si wafer fabrication technology. The design and performance of individual bolometers, using doped layers with a thickness in the range 0.2 to 2 μm are described. The use of epitaxial growth to replace ion implantation for improved performance is discussed. For future use in space based X-ray astronomy, such devices could be fabricated as complete one or two dimensional arrays with integrated isolation and support. The proposed fabrication method for such arrays is outlined