Cosmology and Static Spherically Symmetric solutions in D-dimensional Scalar Tensor Theories: Some Novel Features

We consider scalar tensor theories in D-dimensional spacetime, D \ge 4. They consist of metric and a non minimally coupled scalar field, with its non minimal coupling characterised by a function. The probes couple minimally to the metric only. We obtain vacuum solutions - both cosmological and static spherically symmetric ones - and study their properties. We find that, as seen by the probes, there is no singularity in the cosmological solutions for a class of functions which obey certain constraints. It turns out that for the same class of functions, there are static spherically symmetric solutions which exhibit novel properties: {\em e.g.} near the ``horizon'', the gravitational force as seen by the probe becomes repulsive.Comment: Revtex. 21 pages. Version 2: More references added. Version 3: Issues raised by the referee are addressed. Results unchanged. Title modified; a new subsection and more references added. Verison to appear in Physical Review

A Coupled Experimental and Computational Approach to Quantify Deleterious Hemodynamics, Vascular Alterations, and Mechanisms of Long-Term Morbidity in Response to Aortic Coarctati

Introduction Coarctation of the aorta (CoA) is associated with morbidity despite treatment. Although mechanisms remain elusive, abnormal hemodynamics and vascular biomechanics are implicated. We present a novel approach that facilitates quantification of coarctation-induced mechanical alterations and their impact on vascular structure and function, without genetic or confounding factors. Methods Rabbits underwent thoracic CoA at 10 weeks of age (~ 9 human years) to induce a 20 mm Hg blood pressure (BP) gradient using permanent or dissolvable suture thereby replicating untreated and corrected CoA. Computational fluid dynamics (CFD) was performed using imaging and BP data at 32 weeks to quantify velocity, strain and wall shear stress (WSS) for comparison to vascular structure and function as revealed by histology and myograph results. Results Systolic and mean BP was elevated in CoA compared to corrected and control rabbits leading to vascular thickening, disorganization and endothelial dysfunction proximally and distally. Corrected rabbits had less severe medial thickening, endothelial dysfunction, and stiffening limited to the proximal region despite 12 weeks of normal BP (~ 4 human years) after the suture dissolved. WSS was elevated distally for CoA rabbits, but reduced for corrected rabbits. Discussion These findings are consistent with alterations in humans. We are now poised to investigate mechanical contributions to mechanisms of morbidity in CoA using these methods

Rattus Model Utilizing Selective Pulmonary Ischemia Induces Bronchiolitis Obliterans Organizing Pneumonia

Bronchiolitis obliterans organizing pneumonia (BOOP), a morbid condition when associated with lung transplant and chronic lung disease, is believed to be a complication of ischemia. Our goal was to develop a simple and reliable model of lung ischemia in the Sprague-Dawley rat that would produce BOOP. Unilateral ischemia without airway occlusion was produced by an occlusive slipknot placed around the left main pulmonary artery. Studies were performed 7 days later. Relative pulmonary and systemic flow to each lung was measured by injection of technetium Tc 99m macroaggregated albumin. Histological sections were examined for structure and necrosis and scored for BOOP. Apoptosis was detected by immunohistochemistry with an antibody against cleaved caspase 3. Pulmonary artery blood flow to left lungs was less than 0.1% of the cardiac output, and bronchial artery circulation was ~2% of aortic artery flow. Histological sections from ischemic left lungs consistently showed Masson bodies, inflammation, and young fibroblasts filling the distal airways and alveoli, consistent with BOOP. In quantitative evaluation of BOOP using epithelial changes, inflammation and fibrosis were higher in ischemic left lungs than right or sham-operated left lungs. Apoptosis was increased in areas exhibiting histological BOOP, but there was no histological evidence of necrosis. Toll-like receptor 4 expression was increased in ischemic left lungs over right. An occlusive slipknot around the main left pulmonary artery in rats produces BOOP, providing direct evidence that ischemia without immunomodulation or coinfection is sufficient to initiate this injury. It also affords an excellent model to study signaling and genetic mechanisms underlying BOOP

Jet-Induced Emission-Line Nebulosity and Star Formation in the High-Redshift Radio Galaxy 4C41.17

The high redshift radio galaxy 4C41.17 consists of a powerful radio source in which previous work has shown that there is strong evidence for jet-induced star formation along the radio axis. We argue that nuclear photoionization is not responsible for the excitation of the emission line clouds and we construct a jet-cloud interaction model to explain the major features revealed by the data. The interaction of a high-powered jet with a dense cloud in the halo of 4C41.17 produces shock-excited emission-line nebulosity through ~1000 km/s shocks and induces star formation. The CIII to CIV line ratio and the CIV luminosity emanating from the shock, imply that the pre-shock density in the line-emitting cloud is high enough (~1-10 cm^-3) that shock initiated star formation could proceed on a timescale of order a few x 10^6 yrs, well within the estimated dynamical age of the radio source. Broad (FWHM ~ 100 - 1400 km/s) emission lines are attributed to the disturbance of the gas cloud by a partial bow--shock and narrow emission lines (FWHM ~ 500 - 650 km/s) (in particular CIV) arise in precursor emission in relatively low metallicity gas. The implied baryonic mass ~ 8 \times 10^{10} solar masses of the cloud is high and implies that Milky Way size condensations existed in the environments of forming radio galaxies at a redshift of 3.8. Our interpretation of the data provides a physical basis for the alignment of the radio, emission-line and UV continuum images in some of the highest redshift radio galaxies and the analysis presented here may form a basis for the calculation of densities and cloud masses in other high redshift radio galaxies.Comment: 18 pages, 5 figures; uses astrobib.sty and aaspp4.sty. Better versions of figures available via anonymous from ftp://mso.anu.edu.au:pub/pub/geoff/4C41.1

Mathematical modelling for dynamic analysis of cracked L-shape beam

In this paper, a finite element mathematical model to evaluate natural frequencies and Frequency Response Functions (FRFs) of an L-shaped cracked beam structure is established. Dynamics of L-shaped beam structure is a very challenging subject and very little information is reported in literature. L-shaped beam structure is assumed to be fixed at end of the vertical column and free at the other end of the horizontal column. Natural frequencies are evaluated using finite element method in MatLab and simulations using Ansys (Version 18.2) is carried out to validate the mathematical model. Totally 18 cases with different crack positions and three different crack depths are considered for the analysis. Results obtained by both methods are tabulated and find a very good agreement in the results. Reported results can be used as a benchmark for further study of crack propagation and fatigue failure analysis in built-up structures

Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1)

We study crystal structure, phase transitions and magnetism of pseudo-binary TmxDy1-xAl2 (0 ≤ x ≤ 1) compounds using temperature dependent X-ray powder diffraction, specific heat and magnetization measurements, first principles, and model calculations. In low external magnetic fields, Dy-rich compounds undergo continuous, second-order phase transitions at the respective Curie temperatures, TC. In contrast, the Tm-rich compounds exhibit discontinuous, first-order anomalies in the magnetically ordered states. These sharp transitions correlate with a substantial energy difference between the room temperature cubic and ground state rhombohedral structures of TmAl2. A clear anomaly in the lattice parameter is observed at ∼30 K for x = 0.5, which nearly coincides with TC = 31.2 K. The effective quadrupolar moment of the lanthanides changes sign around x = 0.5, which leads to a nearly zero anisotropy constant and approximately spherical effective 4f charge densities, providing an explanation for the lack of structural distortions below TC for x = 0.5. The calculations confirm [001] as the easy magnetization axis in the ground state tetragonal structure of DyAl2, and reveal collapse of the orbital magnetic moment when the easy magnetization direction changes to [111]. Within the rhombohedral ground state of TmAl2 [111] is the easy magnetization direction

Magnetotransport properties of individual InAs nanowires

We probe the magnetotransport properties of individual InAs nanowires in a field effect transistor geometry. In the low magnetic field regime we observe magnetoresistance that is well described by the weak localization (WL) description in diffusive conductors. The weak localization correction is modified to weak anti-localization (WAL) as the gate voltage is increased. We show that the gate voltage can be used to tune the phase coherence length ($l_\phi$) and spin-orbit length ($l_{so}$) by a factor of $\sim$ 2. In the high field and low temperature regime we observe the mobility of devices can be modified significantly as a function of magnetic field. We argue that the role of skipping orbits and the nature of surface scattering is essential in understanding high field magnetotransport in nanowires

Dynamics of osteoblasts during bone remodeling cycle

Bone is a dynamic connective tissue which adjusts to load variations through continuous bone remodeling, which occurs due to the dynamic behavior of bone cells. Many researchers made attempts in obtaining the dynamic characteristics of osteoblasts and its role in bone remodeling cycle. While making an effort to understand the effects of mechanical stimuli on the osteoblast, certain ambiguity is observed in the past literatures. This paper is to demonstrate the dynamics of osteoblast cells and exhibition of different natural frequencies during its life cycle. Osteoblast is modeled as a frustum of a sphere, considering it as a continuum model. The three prominent parts of an osteoblast, i.e., membrane, cytoplasm and nucleus are considered with reported material properties. Lifespan of an active osteoblast during bone remodeling cycle is considered as 90 days and progressive osteoblast stages are analysed using Ansys. First ten natural frequencies and mode shapes are extracted for nine stages and reported. It is observed that the natural frequencies of a micron sized osteoblast are in the range of kHz. A mathematical relation for the lifespan of an active osteoblast is obtained using curve fitting for fundamental natural frequencies. The natural frequency for exciting an active osteoblast on each particular day during its lifespan can be derived from the relation. This relation can serve as a guiding tool in bioengineering for in vitro bone cell culturing. Results also throw light on the excitation frequency and natural frequency of an osteoblast for proper analysis purpose. The different modes of vibration of osteoblast is identified and reported

The Dynamic Characteristics of a non-linear main landing gear system of an aircraft during landing

The landing gear plays a very important role during landing by absorbing the high impact energy of the aircraft. The main landing gear absorbs the bulk of the load to reduce the load experienced by both the aircraft fuselage and the nose landing gear. In this paper, a mathematical approach is used to extract the dynamic characteristics of the system. A two-degree of freedom mathematical model of the main landing gear is developed. This model is used to derive the dynamic equations of the landing gear system and to study the behaviour of main landing gear during main gear and nose gear touchdown conditions. The non-linear stiffness and damping co-efficient in an Oleo-Pneumatic shock absorber are integrated into the system to achieve a more accurate response of the system. The response of this system is established by adopting a complex modal analysis approach to account for the non-classical damping exhibited by the system. The obtained spring force, damping force and responses are reported. This work provides an alternative approach using complex modal analysis to obtain results for complex systems exhibiting non-linear characteristics