On the Curvature of Rotating Objects

In this paper, we investigate a certain property of curvature which differs in a remarkable way between Lorentz geometry and Euclidean geometry. In a certain sense, it turns out that rotating topological objects may have less curvature (as measured by integrating the square of the scalar curvature) than non-rotating ones. This is a consequence of the indefinite metric used in relativity theory. The results in this paper are mainly based of computer computations, and so far there is no satisfactory underlying mathematical theory. Some open problems are presented.

Probabilistic Cosmology

In this paper, an alternative approach to cosmology is discussed. Rather than starting from the field equations of general relativity, one can investigate the probability space of all possible universes and try to decide what kind of universe is the most probable one. Here two quite different models for this probability space are presented: the combinatorial model and the random curvature model. In addition, it is briefly discussed how these models could be applied to explain two fundamental problems of cosmology: Time’s Arrow and the accelerating expansion.

Rotating Classical Strings

It is a starting point in string theory to assume that elementary particles are in fact rotating strings, and the final goal of the theory is a complete description of fundamental physics, including general relativity. This paper is instead concerned with the reversed question: starting from general relativity, is there a good way to motivate why rotating strings should be more natural models for elementary particles than, say, spherical particles or point-particles? Also, the purpose here is not to motivate full string theory. For example, no hidden dimensions come into play, only the four usual ones, and strings are defined in a very simple geometric way. Rather, the focus is on investigating an interesting mathematical property, which implies that strings may have special features with respect to rotation which spherically symmetric particles have not. In particular, it turns out that in a certain sense rotating strings are simpler than non-rotating ones. This is a consequence of the indefinite metric, and the main result states that the curvature of a non-rotating string, as measured by the square of the scalar curvature, may be reduced by letting it rotate in an appropriate way. The calculations underlying this theorem are heavy and have partly been car-ried out using Mathematica, although in principle the essential theorem may not require super-human labour.

Accelerating Expansion in a Closed Universe

In this paper, I suggest a possible explanation for the accelerating expansion of the universe. This model does not require any dark energy or quintessence. Rather, the idea is to suggest a different view on the origin of general relativity. Since it is very difficult to say something in general, I will mainly restrict myself to the case of very low curvature. The question about the underlying reasons for the acceleration is also closely related to the question whether the universe is a finite or infinite. It is part of the purpose of this paper to argue that a phase of accelerating expansion may be very well compatible with the idea of a closed universe.

Time’s Arrow in a Finite Universe

In this paper, a simple model for a closed multiverse as a finite probability space is analyzed. For each moment of time on a discrete time-scale, only a finite number of states are possible and hence each possible universe can be viewed as a path in a huge but finite graph. By considering very general statistical assumptions, essentially originating from Boltzmann, we make the set of all such paths (the multiverse) into a probability space, and argue that under certain assumptions, the probability for a monotonic behavior of the entropy is enormously much larger then for a behavior with low entropy at both ends. The methods used are just very simple combinatorial ones, but the conclusion suggests that we may live in a multiverse which from a global point of view is completely time-symmetric in the sense that universes with Time’s Arrow directed forwards and backwards are equally probable. However, for an observer confined to just one universe, time will still be asymmetric.

对全球环境酸化问题的展望

1.前言当前环境酸化已认为是当今世界上最严重环境问题之一。很明显在欧洲及北美东部等高度工业化地区,化学气候与地表水和陆地生态系统都发生了重大变化。人为向大气层排放大量的硫、氮氧化物是环境酸化的主要原因。因为,这些化合物以及它们形成的二次空气污染物,在空气中平均滞留时间只不过几天。

双侧视神经发育不良盲儿的认知及行为特征

Aim: To describe cognitive and behavioural characteristics in a group of blind children with bilateral optic nerve hypoplasia (ONH). Methods: Data from records, parents, teachers, and repeated developmental assessments of 13 blind children with ONH born in 1988-1998 were analysed. All children had neuroimaging and/or hormonal evidence of midline malformations. They were all blind and able to communicate with speech. Results: Severe mood swings and temper tantrums were common, especially during the first years of life. Later in life, sluggish tempo, low frustration tolerance and a narrow range of interests were common. Autism had been diagnosed in 6/13 children, autistic-like condition (ALC) was found in another three. The behaviour of the remaining four children was not within the autism spectrum. Eight children had cognitive capacities within the normal or near- normal range; five had mental retardation. Autism/ALC was found in all cognitive subgroups. All children exhibited fluent speech and, of these, 12 had started to talk at the expected age, but had clear deficiencies in communicative ability. Conclusion: These children had a common pattern of behavioural characteristics including autism spectrum disorders independent of intellectual capacities.

多瑙河博斯-大毛罗什堤坝的环境影响

1.前言就在10年前,还将水力发电站宣传是一种最廉价、最洁净的能源生产方式。随后,莱因河、多瑙河、罗讷河。

Seasonal distribution of inhaled allergens in allergic asthma patients with or without allergic rhinitis

To the Editor:Allergic asthma and allergic rhinitis(AR)are common diseases that often occur concomitantly.Approximately 80%of allergic asthmas suffer from AR symptoms,as the two diseases share common immunopathological mechanisms.Sensitizationand exposure to allergens are the risk factors that induce and aggravate allergic airway diseases such as allergic asthma and AR.