Ricci Collineations for Non-Degenerate, Diagonal and Spherically Symmetric Ricci Tensors

The expression of the vector field generator of a Ricci Collineation for diagonal, spherically symmetric and non-degenerate Ricci tensors is obtained. The resulting expressions show that the time and radial first derivatives of the components of the Ricci tensor can be used to classify the collineation, leading to 64 families. Some examples illustrate how to obtain the collineation vector

The effect of estrogen compared to estrogen plus progesterone on the exercise electrocardiogram

AbstractObjectivesThe objective of this study was to evaluate the effect of estrogen compared to estrogen plus progesterone on the stress electrocardiogram (ECG) in relationship to stress-gated myocardial perfusion imaging (MPI) in postmenopausal women.BackgroundIt is generally recognized that estrogen may cause false positive ST depressions on the stress ECG. The effects of estrogen plus progesterone are not known. This study was performed to define the effects of these agents on the stress ECG correlated with results from MPI.MethodsWe evaluated 140 postmenopausal women—31 not taking any hormone replacement therapy (HRT); 75 taking estrogen alone; and 34 taking estrogen plus progesterone. Women with a history of coronary artery disease (CAD), cardiomyopathy, or an abnormal resting ECG were excluded. All women underwent a symptom-limited treadmill test and MPI.ResultsThe overall sensitivity and specificity of the stress ECG compared to MPI in women not taking HRT was 54% and 78%, respectively. In women taking estrogen or estrogen plus progesterone, the sensitivity was unchanged. The power to detect clinically meaningful sensitivity difference (10%) was poor (p = 0.09). The specificity was reduced to 46% (p < 0.01) in women on estrogen therapy. In women taking estrogen plus progesterone, specificity was 80%.ConclusionsOur results suggest that estrogen increases the false positive rate of the stress ECG. This decreased specificity is countered by co-administration of progesterone. Nonetheless, because the sensitivity of the stress ECG is only 50% to 57% in postmenopausal women, women at risk should have imaging in conjunction with stress for the optimal detection of CAD

Imaging for Diagnosis and Monitoring of Cardiac Sarcoidosis

Sarcoidosis is a granulomatous condition, primarily affecting the lungs and thoracic lymph nodes. Clinical cardiac involvement might occur in 2 to 5% of patients with sarcoidosis, and can be associated with serious complications including heart block, cardiomyopathy, ventricular arrhythmias, and potentially death. Timely diagnosis helps initiate treatment before cardiac damage becomes irreversible. In this brief review, we discuss imaging updates for diagnosis and monitoring of cardiac sarcoidosis

Lie and Noether symmetries of geodesic equations and collineations

The Lie symmetries of the geodesic equations in a Riemannian space are computed in terms of the special projective group and its degenerates (affine vectors, homothetic vector and Killing vectors) of the metric. The Noether symmetries of the same equations are given in terms of the homothetic and the Killing vectors of the metric. It is shown that the geodesic equations in a Riemannian space admit three linear first integrals and two quadratic first integrals. We apply the results in the case of Einstein spaces, the Schwarzschild spacetime and the Friedman Robertson Walker spacetime. In each case the Lie and the Noether symmetries are computed explicitly together with the corresponding linear and quadratic first integrals.Comment: 19 page

Youth Driven Engagement in the Homestay Program

Community-based tourism (CBT) is one of the tourist attracting ways involving local community which aims to develop and to enhance the era as well as to bring renewal to the local community. It includes the involvement of youth. CBT comes in various types and this study was conducted to find how CBT can create youth engagement in the homestay program. There were various factors that motivate youth to participate in homestay program. This study involved one case study of a qualitative study conducted in a district in Sabah, namely in Kundasang. In this study, Mersilou Homestay and Walai Tokou Homestay were chosen to be used as a place of study to review factors youth engagement in the homestay program. Data collection was through interviews in partial structures. Data were analyzed using NviVo 10 software and based on certain themes. The findings shown that there were several factors which drive engagement of youth in the homestay program in terms of interests, income, parental encouragement and comfort working in their own areas. In conclusion, the engagement of youth in the homestay program is based on the factors discovered in the study

Conformal Ricci collineations of static spherically symmetric spacetimes

Conformal Ricci collineations of static spherically symmetric spacetimes are studied. The general form of the vector fields generating conformal Ricci collineations is found when the Ricci tensor is non-degenerate, in which case the number of independent conformal Ricci collineations is \emph{fifteen}; the maximum number for 4-dimensional manifolds. In the degenerate case it is found that the static spherically symmetric spacetimes always have an infinite number of conformal Ricci collineations. Some examples are provided which admit non-trivial conformal Ricci collineations, and perfect fluid source of the matter

Positive impact of low-dose, high-energy radiation on bone in partial- and/or full-weightbearing mice

Astronauts traveling beyond low Earth orbit will be exposed to galactic cosmic radiation (GCR); understanding how high energy ionizing radiation modifies the bone response to mechanical unloading is important to assuring crew health. To investigate this, we exposed 4-mo-old female Balb/cBYJ mice to an acute space-relevant dose of 0.5 Gy 56Fe or sham (n = ~8/group); 4 days later, half of the mice were also subjected to a ground-based analog for 1/6 g (partial weightbearing) (G/6) for 21 days. Microcomputed tomography (µ-CT) of the distal femur reveals that 56Fe exposure resulted in 65-78% greater volume and improved microarchitecture of cancellous bone after 21 d compared to sham controls. Radiation also leads to significant increases in three measures of energy absorption at the mid-shaft femur and an increase in stiffness of the L4 vertebra. No significant effects of radiation on bone formation indices are detected; however, G/6 leads to reduced % mineralizing surface on the inner mid-tibial bone surface. In separate groups allowed 21 days of weightbearing recovery from G/6 and/or 56Fe exposure, radiation-exposed mice still exhibit greater bone mass and improved microarchitecture vs. sham control. However, femoral bone energy absorption values are no longer higher in the 56Fe-exposed WB mice vs. sham controls. We provide evidence for persistent positive impacts of high-LET radiation exposure preceding a period of full or partial weightbearing on bone mass and microarchitecture in the distal femur and, for full weightbearing mice only and more transiently, cortical bone energy absorption values

Fibroblast Growth Factor 23 in Long-Duration Spaceflight

Many nutritional factors influence bone, from the basics of calcium and vitamin D, to factors which influence bone through acid/base balance, including protein, sodium, and more. Fibroblast growth factor 23 (FGF23) is a recently identified factor, secreted from osteocytes, which is involved in classic (albeit complex) feedback loops controlling phosphorus homeostasis through both vitamin D and parathyroid hormone (PTH) (1, 2). As osteocytes are gravity sensing cells, it is important to determine if there are changes in FGF23 during spaceflight. In extreme cases, such as chronic kidney disease, FGF23 levels are highly elevated. FGF23 imbalances, secondary to dietary influences, may contribute to skeletal demineralization and kidney stone risk during spaceflight

Fibroblast Growth Factor-23 in Bed Rest and Spaceflight

Many nutritional factors influence bone, from the basics of calcium and vitamin D, to factors which influence bone through acid/base balance, including protein, sodium, and more. Fibroblast growth factor 23 (FGF23) is a recently identified factor, secreted from osteocytes, which is involved in classic (albeit complex) feedback loops controlling phosphorus homeostasis through both vitamin D and parathyroid hormone (PTH) (1, 2). As osteocytes are gravity sensing cells, it is important to determine if there are changes in FGF23 during spaceflight. In extreme cases, such as chronic kidney disease, FGF23 levels are highly elevated. FGF23 imbalances, secondary to dietary influences, may contribute to skeletal demineralization and kidney stone risk during spaceflight. Presented with an imbalanced dietary phosphorus to calcium ratio, increased secretion of FGF23 will inhibit renal phosphorus reabsorption, resulting in increased excretion and reduced circulating phosphorus. Increased intake and excretion of phosphorus is associated with increased kidney stone risk in both the terrestrial and microgravity environments. Highly processed foods and carbonated beverages are associated with higher phosphorus content. Ideally, the dietary calcium to phosphorus ratio should be at minimum 1:1. Nutritional requirements for spaceflight suggest that this ratio not be less than 0.67 (3), while the International Space Station (ISS) menu provides 1020 mg Ca and 1856 mg P, for a ratio of 0.55 (3). Subjects in NASA's bed rest studies, by design, have consumed intake ratios much closer to 1.0 (4). FGF23 also has an inhibitory influence on PTH secretion and 1(alpha)-hydroxylase, both of which are required for activating vitamin D with the conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D. Decreased 1,25-dihydroxyvitamin D will result in decreased intestinal phosphorus absorption, and increased urinary phosphorus excretion (via decreased renal reabsorption). Should a decrease in 1,25- dihydroxyvitamin D be necessary to reduce intestinal phosphorus absorption, calcium absorption will also proportionally be reduced, potentially leading to skeletal demineralization. Demineralization of bone can increase kidney stone risk, a medical issue that could prove detrimental to mission success. Given the interrelationships described above, we sought to determine circulating FGF23 concentrations in spaceflight and ground analog studies to better understand the potential effects of dietary phosphorus on bone and calcium metabolism. We analyzed serum from ISS astronauts participating in studies of bone biochemistry, including the Nutrition SMO and Pro K experiments, and we also evaluated FGF23 during extended-duration bed rest. Serum intact FGF23 levels were determined using an ELISA kit from Kainos laboratories in Japan. While initial evaluation of the data showed no changes over time during flight or bed rest, evaluation continues of FGF23 data in light of dietary factors, PTH, vitamin D status, and other biochemical and endocrine factors