Distant Future (distant + future)

Distribution by Scientific Domains


Selected Abstracts


Distant future of the Sun and Earth revisited

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
K.-P. Schröder
ABSTRACT We revisit the distant future of the Sun and the Solar system, based on stellar models computed with a thoroughly tested evolution code. For the solar giant stages, mass loss by the cool (but not dust-driven) wind is considered in detail. Using the new and well-calibrated mass-loss formula of Schröder & Cuntz, we find that the mass lost by the Sun as a red giant branch (RGB) giant (0.332 M,, 7.59 Gyr from now) potentially gives planet Earth a significant orbital expansion, inversely proportional to the remaining solar mass. According to these solar evolution models, the closest encounter of planet Earth with the solar cool giant photosphere will occur during the tip-RGB phase. During this critical episode, for each time-step of the evolution model, we consider the loss of orbital angular momentum suffered by planet Earth from tidal interaction with the giant Sun, as well as dynamical drag in the lower chromosphere. As a result of this, we find that planet Earth will not be able to escape engulfment, despite the positive effect of solar mass loss. In order to survive the solar tip-RGB phase, any hypothetical planet would require a present-day minimum orbital radius of about 1.15 au. The latter result may help to estimate the chances of finding planets around white dwarfs. Furthermore, our solar evolution models with detailed mass-loss description predict that the resulting tip-AGB (asymptotic giant branch) giant will not reach its tip-RGB size. Compared to other solar evolution models, the main reason is the more significant amount of mass lost already in the RGB phase of the Sun. Hence, the tip-AGB luminosity will come short of driving a final, dust-driven superwind, and there will be no regular solar planetary nebula (PN). The tip-AGB is marked by a last thermal pulse, and the final mass loss of the giant may produce a circumstellar (CS) shell similar to, but rather smaller than, that of the peculiar PN IC 2149 with an estimated total CS shell mass of just a few hundredths of a solar mass. [source]


Disc structure function and its potential for repair

INTERNATIONAL JOURNAL OF RHEUMATIC DISEASES, Issue 1 2002
J. Melrose
The intervertebral disc (IVD) is the largest predominantly avascular, aneural, alymphatic structure of the human body. It provides articulation between adjoining vertebral bodies and also acts as a weight-bearing cushion dissipating axially applied spinal loads. The IVD is composed of an outer collagen-rich annulus fibrosus (AF) and a central proteoglycan (PG)-rich nucleus pulposus (NP). Superior and inferior cartilaginous endplates (CEPs), thin layers of hyaline-like cartilage, cover the ends of the vertebral bodies. The AF is composed of concentric layers (lamellae) which contain variable proportions of type I and II collagen, this tissue has high tensile strength. The NP in contrast is a gelatinous PG-rich tissue which provides weight-bearing properties to the composite disc structure. With the onset of age, cells in the NP progressively die as this tissue becomes depleted of PGs, less hydrated and more fibrous as the disc undergoes an age-dependent fibrocartilaginous transformation. Such age-dependent cellular and matrix changes can decrease the discs' biomechanical competence and trauma can further lead to failure of structural components of the disc. Annular defects are fairly common and include vertebral rim-lesions, concentric (circumferential) annular tears (separation of adjacent annular lamellae) and radial annular tears (clefts which initiate within the NP). While vascular in-growth around annular tears has been noted, evidence from human post-mortem studies indicate they have a limited ability to undergo repair. Several experimental approaches are currently under evaluation for their ability to promote the repair of such annular lesions. These include growth of AF fibrochondrocytes on a resorbable polycaprolactone (PCL) bio-membrane.1 Sheets of fibrochondrocytes lay down type-I collagen and actin stress fibres on PCL. These matrix components are important for the spatial assembly of the collagenous lamella during annular development and correct phenotypic expression of cells in biomatrices.1 An alternative approach employs preparation of tissue engineered IVDs where AF and NP cells are separately cultured in polyglycolic acid and sodium alginate biomatrices, either separately or within a manifold designed to reproduce the required IVD dimensions for its use as a prospective implant device.2 AF and NP cells have also been grown on tissue culture inserts after their recovery from alginate bead culture to form plugs of tissue engineered cartilage.3 A key component in this latter strategy was the stimulation of the high density disc cell cultures with osteogenic protein-1 (OP-1) 200 ng/mL.3 This resulted in the production of tissue engineered AF and NP plugs with compositions, histochemical characteristics and biomechanical properties approaching those of the native disc tissues.2,3 Such materials hold reat promise in future applications as disc or annular implants. The introduction of appropriate genes into disc cells by gene transduction methodology using adenoviral vectors or ,gene-gun' delivery systems also holds considerable promise for the promotion of disc repair processes.4 Such an approach with the OP-1 gene is particularly appealing.5 The anchoring of discal implants to vertebral bodies has also been evaluated by several approaches. A 3D fabric based polyethylene biocomposite holds much promise as one such anchorage device6 while biological glues used to seal fibrocartilaginous structures such as the AF and meniscus8 following surgical intervention, also hold promise in this area. Several very promising new experimental approaches and strategies are therefore currently under evaluation for the improvement of discal repair. The aforementioned IVD defects are a common cause of disc failure and sites of increased nerve in-growth in symptomatic IVDs in man and are thus often sources of sciatic-type pain. Annular defects such as those described above have formerly been considered incapable of undergoing spontaneous repair thus a clear need exists for interventions which might improve on their repair. Based on the rapid rate of progress and the examples outlined above one may optimistically suggest that a successful remedy to this troublesome clinical entity will be developed in the not so distant future. References 1JohnsonWEBet al. (2001) Directed cytoskeletal orientation and intervertebral disc cell growth: towards the development of annular repair techniques. Trans Orthop Res Soc26, 894. 2MizunoHet al. (2001) Tissue engineering of a composite intervertebral disc. Trans Orthop Res Soc26, 78. 3MatsumotoTet al. (2001) Formation of transplantable disc shaped tissues by nucleus pulposus and annulus fibrosus cells: biochemical and biomechanical properties. Trans Orthop Res Soc26, 897. 4NishidaKet al. (2000) Potential applications of gene therapy to the treatment of intervertebral disc disorders. Clin Orthop Rel Res379 (Suppl), S234,S241. 5MatsumotoTet al. (2001) Transfer of osteogenic protein-1 gene by gene gun system promotes matrix synthesis in bovine intervertebral disc and articular cartilage cells. Trans Orthop Res Soc26, 30. 6ShikinamiY , Kawarada (1998) Potential application of a triaxial three-dimensional fabric (3-DF) as an implant. Biomaterials19, 617,35. [source]


The Insecure Social Protection of Migrant Workers From the Maghreb

INTERNATIONAL SOCIAL SECURITY REVIEW, Issue 2 2000
Abdellah Boudahrain
Is it possible to speak of just and equitable social protection for the active populations of poor countries which suffer from development problems and are dominated by an international order in which only the law of the strongest prevails, especially when those populations emigrate to seek work in order to live or merely to survive? Universal standards that are supposed to ensure some measure of international coordination of national legislation and practice in social security between developed countries and the so-called developing countries suffer from this somewhat original form of inequality. The adaptation of such standards at the bilateral, regional and multilateral levels only reflects the discrimination and selfish interests of States and of the rich and powerful, and indeed of broad sectors of their civil society who reject others simply because of their different culture and traditions. The debate is more involved than at first it may seem. By accepting others as being like oneself one can imagine a better world in which, when people move freely - including migrant workers and their families - they enjoy effective protection through social security. A study of the situation of Maghreb migrants employed and residing in western Europe and the Gulf States has much to teach us in this respect, especially in determining whether any form of solidarity is plausible or achievable in some not too distant future. [source]


Distant future of the Sun and Earth revisited

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
K.-P. Schröder
ABSTRACT We revisit the distant future of the Sun and the Solar system, based on stellar models computed with a thoroughly tested evolution code. For the solar giant stages, mass loss by the cool (but not dust-driven) wind is considered in detail. Using the new and well-calibrated mass-loss formula of Schröder & Cuntz, we find that the mass lost by the Sun as a red giant branch (RGB) giant (0.332 M,, 7.59 Gyr from now) potentially gives planet Earth a significant orbital expansion, inversely proportional to the remaining solar mass. According to these solar evolution models, the closest encounter of planet Earth with the solar cool giant photosphere will occur during the tip-RGB phase. During this critical episode, for each time-step of the evolution model, we consider the loss of orbital angular momentum suffered by planet Earth from tidal interaction with the giant Sun, as well as dynamical drag in the lower chromosphere. As a result of this, we find that planet Earth will not be able to escape engulfment, despite the positive effect of solar mass loss. In order to survive the solar tip-RGB phase, any hypothetical planet would require a present-day minimum orbital radius of about 1.15 au. The latter result may help to estimate the chances of finding planets around white dwarfs. Furthermore, our solar evolution models with detailed mass-loss description predict that the resulting tip-AGB (asymptotic giant branch) giant will not reach its tip-RGB size. Compared to other solar evolution models, the main reason is the more significant amount of mass lost already in the RGB phase of the Sun. Hence, the tip-AGB luminosity will come short of driving a final, dust-driven superwind, and there will be no regular solar planetary nebula (PN). The tip-AGB is marked by a last thermal pulse, and the final mass loss of the giant may produce a circumstellar (CS) shell similar to, but rather smaller than, that of the peculiar PN IC 2149 with an estimated total CS shell mass of just a few hundredths of a solar mass. [source]


Making the biodiversity monitoring system sustainable: Design issues for large-scale monitoring systems

AUSTRAL ECOLOGY, Issue 1 2004
IAN WATSON
Abstract There is strong demand for information about the status of, and trends in, Australia's biodiversity. Almost inevitably, this demand for information has led to demand for a broad-scale monitoring system. However, the decision to embark on a monitoring system should only be made once it has been established that a monitoring system is the optimal way to inform management. We stress the need to invest resources in assessing whether a monitoring system is necessary before committing resources to the design and implementation of the system. Current debate associated with the design of a biodiversity monitoring system has similarities to the debate within the range management profession in the early 1970s. The experience with range monitoring shows that large-scale monitoring systems such as those being proposed will require considerable resources, recurrently expended into the distant future, but with only a limited ability to adapt to new demands. Those involved in any biodiversity monitoring system will need to understand the implications of investing in a long-term monitoring programme. Monitoring sustainability will only be possible if the monitoring system is itself sustainable. We discuss a number of issues that need to be addressed before the system is at all sustainable. These attributes are a mix of biophysical, social and institutional attributes and highlight the view that monitoring systems of the type being suggested comprise an unusual mixture of attributes not found in typical scientific activity. The present paper is not a technical manual, but rather considers some of the design issues associated with designing and implementing large-scale monitoring systems. [source]


Virtual education in universities: a technological imperative

BRITISH JOURNAL OF EDUCATIONAL TECHNOLOGY, Issue 5 2001
John O'Donoghue
Many educational journals have debated the issue of the "virtual university". As technology is improving and evolving, such "virtuality" becomes a reality. The forecasts are that, in the not too distant future, it will be possible for courses to be completed solely by the use of the World Wide Web or Internet. These "virtual classrooms" will take the place of the solid buildings where students currently attend lectures, at set times in set rooms. The information will be gathered at the student's convenience and assignments will be handed in via this medium. There is potentially an advantage for everyone involved, from the reduced building resource costs to the availability of teaching support 24 hours a day, 7 days a week Whilst many of these studies identify the benefits of technology in education there are dissenting voices from many other quarters. However there are also arguments identifying the disadvantages to the technology based delivery systems proposed. Either way, there are going to be radical changes in the methods which students will use to tackle the workload involved in studying towards a degree. This paper will explore both sides of the argument. The main contention of this paper is that technology undoubtedly will offer many benefits for the learner, however, the pitfalls need careful consideration in the design of the learning environment. This paper uses examples from educational institutions across different cultures. [source]


Subtype-selective targeting of voltage-gated sodium channels

BRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2009
Steve England
Voltage-gated sodium channels are key to the initiation and propagation of action potentials in electrically excitable cells. Molecular characterization has shown there to be nine functional members of the family, with a high degree of sequence homology between the channels. This homology translates into similar biophysical and pharmacological properties. Confidence in some of the channels as drug targets has been boosted by the discovery of human mutations in the genes encoding a number of them, which give rise to clinical conditions commensurate with the changes predicted from the altered channel biophysics. As a result, they have received much attention for their therapeutic potential. Sodium channels represent well-precedented drug targets as antidysrhythmics, anticonvulsants and local anaesthetics provide good clinical efficacy, driven through pharmacology at these channels. However, electrophysiological characterization of clinically useful compounds in recombinant expression systems shows them to be weak, with poor selectivity between channel types. This has led to the search for subtype-selective modulators, which offer the promise of treatments with improved clinical efficacy and better toleration. Despite developments in high-throughput electrophysiology platforms, this has proven very challenging. Structural biology is beginning to offer us a greater understanding of the three-dimensional structure of voltage-gated ion channels, bringing with it the opportunity to do real structure-based drug design in the future. This discipline is still in its infancy, but developments with the expression and purification of prokaryotic sodium channels offer the promise of structure-based drug design in the not too distant future. [source]