Formation Of Remnants Research Articles

Winning the battle against childhood physical inactivity

pathogenesis of age-related bone loss show that most bone loss with age is cortical, not trabecular, and is the result of intracortical remodelling on the surfaces of the myriads of haversian canals traversing the cortex. These excavated canals increase in number, size and coalesce, particularly in the cortex adjacent to the marrow space leaving a layer of chaotically connected cortical remnants that look like trabeculae. Half of the total bone loss that occurs during ageing is produced during the process of formation of cortical remnants; indeed, the ratio of the thickness of the layer of cortical remnants to the thickness of the entire cortical mass (proportion compact remnants; PCR) appears to be a more reliable indicator of age-related bone loss than the cortical thickness. The calculation of porosity in the compactappearing cortex without including porosity produced by cortical remnants underestimates the true age related increase in porosity by three-fold. Moreover, the true decline with age is underestimated fourfold when cortical remnants are erroneously included in the trabecular compartments as is commonly done in standard bone structure analyses. Thus, overlooking intracortical porosity producing cortical remnants has resulted in a significant underestimation of agerelated cortical decay and loss.Contrary to prevailing notions, most bone loss is cortical, occurs by intracortical remodelling, causes most structural decay, and occurs after 60 years of age, not in the decade after menopause. Intracortical remodelling is a neglected target for preventing and reversing bone fragility in old age.

Evolution of the X-ray luminosity in young H ii galaxies

In an effort to understand the correlation between X-ray emission and present star formation rate (SFR), we obtained XMM-Newton data to estimate the X-ray luminosities of a sample of actively starforming HII galaxies. The obtained X-ray luminosities are compared to other well known tracers of star formation activity such as the far infrared and the ultraviolet luminosities. We also compare the obtained results with empirical laws from the literature and with recently published analysis applying synthesis models. We use the time delay between the formation of the stellar cluster and that of the first X-ray binaries, in order to put limits on the age of a given stellar burst. We conclude that the generation of soft X-rays, as well as the Ha or infrared luminosities is instantaneous. The relation between the observed radio and hard X-ray luminosities, on the other hand, points to the existence of a time delay between the formation of the stellar cluster and the explosion of the first massive stars and the consequent formation of supernova remnants and high mass X-ray binaries (HMXB) which originate the radio and hard X-ray fluxes respectively. When comparing hard X-rays with a star formation indicator that traces the first million years of evolution (e.g. Ha luminosities) we found a deficit in the expected X-ray luminosity. This deficit is not found when the X-ray luminosities are compared with infrared luminosities, a star formation tracer that represents an average over the last 10^8 years. The results support the hypothesis that hard X-rays are originated in X-ray binaries which, as supernova remnants, have a formation time delay of a few mega years after the starforming burst.

THE STOCKHOLM 20-YEAR FOLLOW-UP OF ANEURYSMAL SUBARACHNOID HEMORRHAGE OUTCOME

To assess the clinical and radiological long-term outcome after aneurysmal subarachnoid hemorrhage (SAH) in a defined referral area regarding recurrent SAH and de novo aneurysm formation. One hundred and two 1-year survivors after aneurysmal SAH, who were treated at the Neurosurgical Clinic, South Hospital, Stockholm, Sweden, between 1983 and 1985, were followed for 20 years. Forty-nine surviving patients were reevaluated. Hospital records and death certificates were scrutinized for all 53 nonsurviving patients. Clinical history penetration, Mini Mental Status, Rankin Disability Score, and Barthel Index were used to evaluate the outcome. Computed tomographic angiography was used to investigate the cerebral arteries. One hundred and two patients were traced. Fifty-three patients were deceased. One patient had a hospital record of sustaining an aneurysmal SAH from a known but not clipped aneurysm. Three patients had nonaneurysmal intracerebral hemorrhage and two sustained traumatic SAH. There were 49 surviving patients. Six refused follow-up. None of these patients had hospital records of intracranial disease. Three of the 43 remaining patients could not be tested. None of the survivors had experienced a new SAH. Aneurysm base remnants were observed in 1% (eight patients, 790 person-years of follow-up) and de novo aneurysms were observed in 0.9% (seven patients, 790 person-years of follow-up). From this epidemiological survey of patients with aneurysmal SAH, it was found that none of the patients experienced a recurrent subarachnoid bleed from the treated aneurysm during a 20-year follow-up period. Thus, a routine extreme long-term follow-up period is not necessary. De novo aneurysm formation and possible enlargements of aneurysm base remnants were observed in almost 2% of patients per person year and should, therefore, be subject of a routine, long-term follow-up.

Measurement and meaning of apolipoprotein AI and apolipoprotein B plasma levels

Apolipoproteins AI and B are structural components of lipoprotein particles, and also determinants of the metabolic fate of the encapsulated lipid, cholesterol and triglyceride. Development of accurate assays for these apolipoproteins has opened the way for their use as predictors of coronary heart disease risk. Interpretation of AI and apo B levels is best undertaken with background knowledge of the metabolic status of an individual, especially the lipolytic capacity as reflected in the triglyceride concentration. Those with raised triglyceride, in general, not only have an elevated apo B/apo AI ratio, but also apo B-containing lipoproteins with a prolonged residence time and hence ample opportunity for modification and damage. Assessment of apolipoprotein levels is an aid to risk prediction and can be useful in tailoring treatment.

Simvastatin causes the formation of cholesterol-rich remnants in mice lacking apoE

Mice that lack apolipoprotein E (apoE) display a severe hypercholesterolemia, caused by the accumulation of apolipoprotein B-48 (apoB-48)-carrying remnants of chylomicrons and very-low-density lipoproteins in the plasma. Statins are potent inhibitors of cholesterol synthesis that, when administered to mice lacking apoE, cause paradoxical further increases in plasma cholesterol levels. In the present study, we examined the mechanisms responsible for this phenomenon. ApoE-deficient mice fed a chow diet containing simvastatin developed, as anticipated, an enhanced increase in plasma cholesterol and a decrease in plasma triglycerides. Fractionation of the plasma lipoproteins by FPLC revealed that the lipid changes were confined to the lipoprotein remnants. Western blot analysis of the remnants from the untreated and simvastatin-treated mice showed no differences in their apoB-48 content, indicating that both groups of animals accumulated similar numbers of remnant particles in the plasma. Following the injection of Triton WR-1339, the simvastatin-treated mice accumulated in the plasma significantly more cholesterol and significantly less triglycerides than the untreated animals. These results indicate that the enhanced hypercholesterolemia observed in apoE-deficient mice treated with simvastatin is not the result of an increased number of remnant particles in circulation but is caused by synthesis and secretion into the plasma of lipoproteins that are enriched in cholesterol and depleted of triglycerides.

Dual roles of apolipoprotein CI in the Formation of atherogenic remnants

Dual roles of apolipoprotein CI in the Formation of atherogenic remnants

SR-BI-mediated selective lipid uptake segregates apoA-I and apoA-II catabolism

The HDL receptor scavenger receptor class B type I (SR-BI) binds HDL and mediates the selective uptake of cholesteryl ester. We previously showed that remnants, produced when human HDL(2) is catabolized in mice overexpressing SR-BI, become incrementally smaller, ultimately consisting of small alpha-migrating particles, distinct from pre-beta HDL. When mixed with mouse plasma, some remnant particles rapidly increase in size by associating with HDL without the mediation of cholesteryl ester transfer protein, LCAT, or phospholipid transfer protein. Here, we show that processing of HDL(2) by SR-BI-overexpressing mice resulted in the preferential loss of apolipoprotein A-II (apoA-II). Short-term processing generated two distinct, small alpha-migrating particles. One particle (8.0 nm diameter) contained apoA-I and apoA-II; the other particle (7.7 nm diameter) contained only apoA-I. With extensive SR-BI processing, only the 7.7 nm particle remained. Only the 8.0 nm remnants were able to associate with HDL. Compared with HDL(2), this remnant was more readily taken up by the liver than by the kidney. We conclude that SR-BI-generated HDL remnants consist of particles with or without apoA-II and that only those containing apoA-II associate with HDL in an enzyme-independent manner. Extensive SR-BI processing generates small apoA-II-depleted particles unable to reassociate with HDL and readily taken up by the liver. This represents a pathway by which apoA-I and apoA-II catabolism are segregated.

A ULX in NGC 4559: A “Mini-Cartwheel” Scenario?

AbstractWe have studied the peculiar environment around a ULX in NGC 4559 (with Lx ≈ 2 x 1040 erg s–1 and MBH ≳ 50M⊙). The X-ray source is located near the rim of a young (age < 30 Myr), large (diameter ≈ 700 pc) ring-like star forming complex possibly triggered by the impact of a dwarf satellite galaxy through the gas-rich outer disk of NGC 4559. We speculate that galaxy interactions (including the infall of high-velocity clouds and satellites on a galactic disk) and low-metallicity environments offer favourable conditions for the formation of compact remnants more massive than “standard” X-ray binaries, and accreting from a massive Roche-lobe filling companion.

Depositional remnants, part 1: Common components of the stratigraphic record with important implications for hydrocarbon exploration and production

The preservation of sedimentary strata below erosion surfaces can be highly variable laterally, and commonly only small remnants of originally more extensive deposits remain. The concept of remnants is not new, but their abundance and the fact that they commonly develop below low-relief erosion surfaces, as well as below those that incise deeply, may not be fully appreciated. Spatial variations in accommodation because of paleotopography, synsedimentary and penecontemporaneous tectonics, and differential compaction occur on a variety of scales in all settings. In low-accommodation and shallow-shelf settings, spatial variations in accommodation commonly result in the formation of remnants ranging in size from small (few to tens of square kilometers) to basin scale (hundreds of square kilometers). Remnants of porous and permeable facies encased in low-permeability facies are an important and relatively common type of stratigraphic trap. Conceptual models for three scales of remnants are used to illustrate their significance to petroleum exploration and production.The recognition of these deposits, herein referred to as depositional remnants, is commonly critical to systems analysis because stratigraphic terminations caused by erosional truncation must be interpreted differently from those caused by lithofacies change. In addition, the preserved geometry of remnants can be quite different from the geometry of the original deposit, and because geometry is heavily relied upon in interpretations of ancient systems, interpreting a preserved geometry as a geometry can result in significant misunderstandings. Depositional remnants are common in the stratigraphic record and represent an important concept to open up new hydrocarbon plays in mature basins.

The Imprint of Presupernova Evolution on Supernova Remnants

The evolution of Type Ia supernova binary system progenitors is highly uncertain. Several evolutionary models predict that the accretion of mass onto the white dwarf is accompanied by mass ejection from the binary in the form of a powerful wind, but very few observations have been made during the initial phase of formation of supernova remnants, when the interaction of supernova ejecta with presupernova wind could be tested. Here we present hydrodynamical simulations of supernova ejecta interaction with an ambient medium modified by presupernova wind. The structure of the ambient medium when the supernova explodes is very sensitive to the details of wind history, and the evolution of the supernova remnant can be affected during several thousand years. We have found that the forward shock expansion parameter is a good tool for discriminating between several wind models. The evolution of the supernova remnant in the presence of an ambient medium modified by interaction with presupernova wind cannot be described by a similarity solution. We also rule out simple models based on a circumstellar medium that merges smoothly with a uniform density ambient medium.

Evidence of a supernova origin for the black hole in the system GRO J1655 - 40

Stars with masses greater than about ten solar masses are thought to end their lives either in a supernova1 or in a direct gravitational collapse process2, either of which could have a black hole as a remnant. But there is as yet no direct observational evidence to support either gravitational collapse in general or the formation of black hole remnants in particular. Here we report a large overabundance of oxygen, magnesium, silicon and sulphur in the atmosphere of the star orbiting a probable black hole in the binary system GRO J1655-40 (also known as Nova Scorpii 1994). These α-elements are six to ten times more abundant in the star's atmosphere than they are in the Sun's. We interpret these high abundances as evidence for supernova ejecta captured by the companion star. The relative abundances of these elements suggest that the supernova progenitor was in the mass range 25–40 solar masses.

Astrophysical constraints on primordial black hole formation from collapsing cosmic strings

Primordial black holes (PBH) may have formed from the collapse of cosmic string loops. The spectral shape of the PBH mass spectrum can be determined by the scaling argument for string networks. Limits on the spectral amplitude derived from extragalactic γ-ray and galactic γ-ray and cosmic ray flux observations as well as constraints from the possible formation of stable black holes remnants are reanalyzed. The new constraints are remarkably close to those derived from the normalization of the cosmic string model to the cosmic microwave background anisotropies.

The events leading to the formation of ghost remnants from the starch granule surface and the contribution of the granule surface to the gelatinization endotherm

During the process of gelatinization, the external layers of starch granules form granule envelopes which degrade into ghost remnants. These envelopes contribute to the gelatinization endotherm of starch through the controlled dispersion of internal starch polymer. Ghost remnants are shown to be derived from the external layers of the granules for a range of starches with different amylose/amylopectin ratios. The ghost remnants are composed primarily of amylopectin and exhibit elastic/plastic properties. The surface amylopectin is shown to be structurally distinct from internal amylopectin. During the early stages of granule gelatinization, high amylopectin starch granules swell by 200% in size, where the outer layer of the granule forms an envelope surrounding the disrupted internal starch polymers. High amylose starches do not swell, but do form envelopes at high temperatures (≥ 90 °C). At a critical stress point the swollen envelope ruptures becoming a ghost, releasing the majority of the internal starch molecules, while a minority of the starch polymers remain trapped by the collapsed ghost. During the final stages of gelatinization the ruptured envelope degrades into ghost remnants. Manipulation of the starch granule surface, either genetically or chemically, would result in alteration of the gelatinization endotherm.

Limits on black hole formation from cosmic string loops

In theories with cosmic strings, a small fraction of string loops may collapse to form black holes. In this paper, various constraints on such models involving black holes are considered. Hawking radiation from black holes, gamma and cosmic ray flux limits and constraints from the possible formation of stable black hole remnants are reanalyzed. The constraints which emerge from these considerations are remarkably close to those derived from the normalization of the cosmic string model to the cosmic microwave background anisotropies.

Properties of damaged starch granules: composition and swelling properties of maize, rice, pea and potato starch fractions in water at various temperatures

A range of cereal and non-cereal starches (maize, waxy maize, rice, waxy rice, pea and potato) were ball milled to obtain various levels of damage. The susceptibility of the different starches to ball milling-induced damage was related to granule composition, dimensions, size distribution, gelatinization parameters by differential scanning calorimetry, swelling factors determined by dye exclusion, and leaching characteristics of α-glucan from the granules heated in water. The formation of granule remnants, gel-forming material and soluble amylopectin fragments from the damaged starches was investigated and related to gel volume formed at different temperatures.

Chylomicron/chylomicron remnant turnover in humans: evidence for margination of chylomicrons and poor conversion of larger to smaller chylomicron remnants

The size of cholesterol-rich lipoprotein particles is a strong determinant of whether they may be deposited in the arterial wall and by this become potentially atherogenic. This study deals with the in vivo transformation of larger-sized chylomicrons and chylomicron remnants to smaller-sized remnants. Twelve healthy men aged 22 to 45 years were given a fatty meal to which retinyl palmitate (RP) had been added. Plasmapheresis was performed 4 1/2 h after meal intake to isolate approximately 400 ml plasma. The RP-rich plasma was re-injected to the subject 24 h later. The RP content was determined in whole plasma and in Svedberg flotation rate fractions (Sf) > 400, Sf 60-400 and Sf 20-60. A compartmental model was developed for the kinetic analysis. Lipoprotein fractions showed minimal signs of aggregation, thus arguing for well-preserved postprandial lipoproteins. Approximately a fourth [23% (4-68%)] of the RP-containing lipoproteins in the Sf > 400 pool was converted to smaller species (Sf 60-400). Conversion of material from the Sf 60-400 to the Sf 20-60 fraction could not be detected. In a second study a large bolus dose of a triglyceride emulsion (Intralipid) was injected to subjects shortly after the RP-labeled plasma to investigate the endothelial binding of the chylomicron/chylomicron remnants. RP material in the Sf > 400 fraction rapidly returned to plasma, arguing for margination of chylomicrons, whereas the corresponding effect was minimal in the Sf 60-400 and Sf 20-60 fractions. The formation of small chylomicron remnants from the larger chylomicron/chylomicron remnant species is limited and large chylomicron/chylomicron remnants are not evenly distributed in plasma, rather they show signs of being marginated to the vascular endothelium.

Dissipating cosmic vortons and baryogenesis

Grand unified theories can admit cosmic strings with fermion zero modes which result in the string carrying a current and the formation of stable remnants, vortons. We consider theories in which the zero modes do not survive a subsequent phase transition, for example the electroweak transition, resulting in vorton dissipation. The dissipating vortons can create a baryon asymmetry. We calculate the asymmetry produced, and show that it is maximised if the vortons decay just before they dominate the energy density of the Universe. We further bound the asymmetry produced by the late decay of any relic particle.

Modification of the fatty acid composition of dietary oils and fats on incorporation into chylomicrons and chylomicron remnants.

Possible changes in the fatty acid composition of dietary fats and oils which might occur during digestion, absorption and formation of chylomicrons and chylomicron remnants were investigated. Chylomicrons were collected from the thoracic duct of rats tube-fed with olive, maize, palm or fish oil or butter fat, and their fatty acid composition was determined and compared with that of their parent lipids. In turn, these lipoproteins were converted to chylomicron remnants in functionally hepatectomized rats and their composition re-determined. The predominant fatty acids in each of the oils and fats also predominated in their respective chylomicrons, but their proportions were reduced during the processes leading to their formation. Endogenous contributions of linoleic, eicosapentaenoic, and docosahexaenoic acids were particularly noted when these fatty acids were not well-represented in the original oils and fats, suggesting that they may be obligatory constituents in the formation of chylomicrons. The conversion of chylomicrons to remnants further attenuated the extremes in fatty acid composition of the dietary oils and fats. These results indicate that following an acute intake of oil or fat, the resulting chylomicrons and chylomicron remnants presented to the tissues contain a more balanced distribution of saturated, mono- and polyunsaturated fatty acids than the oils and fats from which they were derived.

Role of ribosomes in Semliki Forest virus nucleocapsid uncoating.

The mechanism by which Semliki Forest virus nucleocapsids are uncoated was analyzed in living cells and in vitro. In BHK-21 cells, uncoating occurred with virtually complete efficiency within 1 to 2 min after the nucleocapsids entered the cytoplasm. It was inhibited by monensin, which blocks nucleocapsid penetration from endosomes. As previously shown for Sindbis virus (G. Wengler and G. Wengler, Virology 134:435-442, 1984), the capsid proteins from incoming nucleocapsids became associated with ribosomes. The ribosome-bound capsid proteins were distributed throughout the cytoplasm, while the viral RNA remained associated with vacuolar membranes. Using purified nucleocapsids and ribosomes in vitro, we established that ribosomes alone were sufficient for uncoating. Their role was to release the capsid proteins from nucleocapsids and irreversibly sequester them, in a process independent of energy and translation. The process was stoichiometric rather than catalytic, with a maximum of three to six capsid proteins bound to each ribosome. More than 80% of the capsid proteins could thus be removed from the viral RNA, resulting in the formation of nucleocapsid remnants whose sedimentation coefficients progressively decreased from 140S to 80S as uncoating proceeded.

Hypertriglyceridemia is exacerbated by slow lipolysis of triacylglycerol-rich lipoproteins in fed but not fasted streptozotocin diabetic rats

Hydrolysis by endothelial lipases of triacylglycerol-rich lipoproteins of diabetic origin were compared to lipoproteins of non-diabetic origin. The plasma lipoprotein fraction of density <1.006 g/ml, including chylomicrons and VLDL, were incubated in vitro with post-heparin plasma (PHP) lipases. The lipoproteins of diabetic origin were hydrolysed at a significantly slower rate than lipoproteins from normal rats by the lipoprotein lipase component of PHP. However, if rats were fasted for 16 h prior to lipoprotein recovery, no differences in rates of VLDL hydrolysis were observed. Slower hydrolysis of lipoproteins of diabetic origin reflected a decrease in the apolipoprotein CII/CIII ratio and other changes in the apolipoprotein profile. To assess whether diabetic rats were less able to clear triacylglycerol independent of changes in the nature of the lipoproteins, we monitored the clearance of chylomicron-like lipid emulsions in hepatectomized rats. In vivo, emulsion triacylglycerol hydrolysis was not showed due to diabetes. However, control and diabetic rats, which had been fasted for 16 h, cleared triaclyglycerol at about twice the rate of fed rats. Triaclyglycerol secretion rates in diabetic and control rats were similar, whether fed or fasted. We conclude that in streptozocin diabetic rats, hypertriglyceridemia was not due to overproduction of chylomicron- or VLDL-triaclyglycerol, nor to decreased endothelial lipase activities. Rather, in fed diabetic rats, the triaclyglycerol-rich lipoproteins are poorer substrates for lipoprotein lipase. This may lead to slower formation of remnants which would exacerbate slow remnant removal. VLDL of diabetic origin were hydrolysed as efficiently as VLDL from control donors, suggesting that in the fed state the lipolytic defect may be specific for chylomicrons.