Early studies on the biological effects of high-intensity magnetic fields

In 1892, Frederick Peterson described the experiences of humans exposed to magnetic fields of strength comparable to those currently used in magnetic resonance imaging. These investigations were conducted in the Edison Laboratory. None of the subjects exposed to constant and to time-variable magnetic fields suffered any ill effects. Peterson concluded that the human organism was in no way appreciably affected by the most powerful magnets known to nineteenth-century science. Peterson can be credited with the first truly scientific assessment of the biological effects of high-intensity magnetic fields. His experiments on humans, done one century ago with great cogency and skill, provide a source of inspiration to modern studies on magnetic resonance imaging.     

试论华侨华人学科的形成与定位

华侨华人研究具有确定的研究对象、专门的术语 ,开始形成有特色的研究方法和学术规范。理论体系虽处于不够成熟的阶段 ,但在学科建设的过程中 ,将日趋完善。华侨华人学是一门正在兴起的交叉学科 ,具有跨学科性和多学科性。它既承袭和借用了大量老学科的理论、概念、方法和学术规范 ,同时逐步创造出不依附其他学科的相对独立的学科体系     

The widespread occurrence of Celtic field systems in the central part of the Netherlands

The detailed elevation model based on airborne laser altimetry (AHN) proved to be a reliable tool to detect well-developed Celtic field systems, characteristic arable plots of the Iron Age. They were detected in the central part of the Netherlands, where only a limited number of Celtic field systems have been recognized in the past. Most of these previously detected systems were identified in the northern part of the Netherlands or in the southern part, but not in this zone. About 1200 ha of well-developed systems could be identified by AHN in the central part of the Netherlands, of which only 136 ha were registered as an archaeological monument. Another 335 ha of archaeologically identified Celtic field systems were not accepted or recognized by AHN, because they were morphologically less well-developed. Most of the around 1050 ha new discoveries occur in rough vegetations and forested areas, and can hardly be identified with previously used geodetic methods and aerial photography. Less well-developed or preserved systems were even more extensive and remnants were traced as fossil arable layers below plaggen soils or on lower slopes incorporated in mediaeval reclamations. The newly identified Celtic field systems, therefore, can be considered as remnants of much larger areas once covered with these arable plots. In the central part of the Netherlands, the estimated area once covered was at least around 4500 ha, more than enough to supply 10,000 people with cereals. Well-developed Celtic field systems started to develop in the late Iron Age with formation intensifying during the early Roman Period. The central part of the Netherlands is situated just north of the river Rhine, the former boundary of the Roman Empire, the Limes. The newly discovered extent of Celtic field systems will have influenced the interaction between different cultures on the border of the Roman Empire in the early Roman Period, about which very little is known. This perspective underscores the need for an integrated conservation policy and in-depth research through excavations in the near future.     

Restructuring Beijing's Social Space: Observations on the Olympic Games in 2008

Two American geographers comment on the preceding analysis of restructuring of Beijing's social space (Feng et al., 2007) by presenting observations on the city's Olympic Games, forthcoming in the summer of 2008. The authors focus on some of the more salient geographical impacts stemming from construction, relocation, and related measures undertaken by the authorities to accommodate the event. Included in the paper are sections on environmental concerns (particularly air pollution), infrastructure (water supply, automobile traffic, and mass transit), and relocation and displacement of residents (particularly of migrants and other disadvantaged segments of the population). Journal of Economic Literature, Classification Numbers: I31, O15, O18, P20. 2 figures, 2 tables, 44 references.     

Small-scale fluctuations of magnetic and electric components of the ELF and VLF wave fields in the sub-auroral topside ionosphere : stochastic characteristics of the wave field

When the Interkosmos-14 and Interkosmos-19 satellites crossed the region of spatially varying electron concentration in the topside ionosphere adjacent to the high-latitude boundary of the main ionospheric trough, it was discovered that there were simultaneous fluctuations of plasma density, temperature and the amplitudes (H_x and E_y) of the ELF and VLF radio/plasma emissions. The probability characteristics of the naturally perpendicular H_x and E_y fluctuations are analysed. The correlation coefficient R(_H, E_y) turned out to be less than 0.6 at frequencies of F ⩽ 4.65 kHz, while at higher frequencies R increases, up to 0.9 at 15 kHz. The following interpretations are proposed:

1. 1.1. While measuring noise emissions, as a rule a mixture of numerous elementary waves is recorded.
2. 2.2. At frequencies exceeding the local lower hybrid resonance frequency (in our case f_LHR ≈ 5 kHz), a mixture of electromagnetic waves experiencing the influence of the inhomogeneous electron concentration N_e is registered.
3. 3.3. At frequencies which are lower than the local value f_LHR the mixture mainly consists of ELF waves. The wave field has a complicated structure, and the dynamical coherence between electric and magnetic field components is not as simple as at VLF frequencies (f ≈ 15 kHz).
4. 4.4. It is shown that the wave components for a mixture of electromagnetic and electrostatic waves (for instance a mixture of VLF and lower hybrid frequency waves) have a lower correlation coefficient because the electrostatic waves are unrelated to the electromagnetic waves.
5. 5.5. The correlation analysis offers an opportunity to detect the presence of waves of various types in the wave mixture.

     

Modeling of hydrogen production by serpentinization in ultramafic‐hosted hydrothermal systems: application to the Rainbow field

The production of hydrogen by serpentinization in ultramafic‐hosted hydrothermal systems is simulated by coupling thermodynamic and dynamic modeling in the framework of a thermo‐hydraulic single‐pass model where a high‐temperature hydrothermal fluid moves preferentially through a main canal of high permeability. The alteration of ultramafic rocks is modeled with a first‐order kinetic formulation, wherein the serpentinization rate coefficient, K_r, takes the form: K_r = A exp(?α(T ? T₀)²). In this formulation, α determines the temperature range of the reaction and T₀ is the temperature at which the serpentinization rate reaches its maximum. This model is applied to the Rainbow hydrothermal system, which is situated on the Mid‐Atlantic Ridge, and characterized by a high temperature, a high mass flux, and a very high hydrogen concentration. The results show that a first‐order kinetic law gives a useful representation of the kinetics of serpentinization. The estimated value for the parameter A in the temperature‐dependent formulation of the serpentinization rate coefficient lies in the range (1–5) × 10^?11 s^?1. This effective parameter is several orders of magnitude lower than the values obtained from small grain‐size experiments, but in agreement with other published modeling studies of natural systems. Numerical simulations show that the venting site is able to produce the observed high concentration of hydrogen during the whole continuous lifetime of the Rainbow site.