Cervical vertebral motions and biomechanical responses to direct loading of human head

There is little known data characterizing the biomechanical responses of the human head and neck under direct head loading conditions. However, the evaluation of the appropriateness of current crash test dummy head-neck systems is easily accomplished. Such an effort, using experimental means, generates and provides characterizations of human head-neck response to several direct head loading conditions. Low-level impact loads were applied to the head and face of volunteers and dummies. The resultant forces and moments at the occipital condyle were calculated. For the volunteers, activation of the neck musculature was determined using electromyography (EMG). In addition, cervical vertebral motions of the volunteers have been taken by means of X-ray cineradiography. The Ethics Committee of Tsukuba University approved the protocol of the experiments in advance. External force of about 210 N was applied to the head and face of five volunteers with an average age of 25 for the duration of 100 msec or so, via a strap at one of four locations in various directions: (1) an upward load applied to the chin, (2) a rearward load applied to the chin without facial mask, (3) a rearward load applied to the chin with the facial mask, and (4) a rearward load applied to the forehead. The same impact force as those for the human volunteers was also applied to HY-III, THOR, and BioRID. We found that cervical vertebral motions differ markedly according to the difference in impact loading condition. Some particular characteristics are also found, such as the flexion or extension of the upper cervical vertebrae (C0, C1, and C2) or middle cervical vertebrae (C3-C4), showing that the modes of cervical vertebral motions are markedly different among the different loading conditions. We also found that the biofidelity of dummies to neck response characteristics of the volunteers at the low-level impact loads is in the order of BioRID, THOR, and HY-III. It is relevant in this regard that the BioRID dummy was designed for a low-severity impact environment, whereas THOR and HY-III were optimized for higher-severity impacts.     

Palaeopathological Fish Bones from Phosphorites of the Lake Manyara Area, Northern Tanzania – Fossil Evidence of a Physiological Response to Survival in an Extreme Biocenosis

In Plio/Pleistocene phosphorites at Minjingu, 5 km east of Lake Manyara, northern Tanzania, hyperostotic fish bones (Tilly bones) are preserved, which developed in a strongly alkaline, lacustrine environment. The palaeopathological addition of bony tissue to the normal skeleton of these fishes was analysed with a scanning electron microscope (SEM), in thin sections under ordinary and polarised light, in microradiographs, with epifluorescence microscopy and their fluorine content was determined. The development of these structures is probably correlated with the high content of fluorine in this exceptional environment and denotes a physiological survival strategy in this ancient biocenosis.     

Predicting toxicity using computed molecular topologies: The example of triorganotin compounds

The LC50 values of eight triorganotin compounds for crab zoeae, $\text{Rhithropanopeus}$$\text{harrisii}$ correlate with substituent constants reflecting partitioning effects. Computed molar surface areas predict toxicity as well as any parameter used suggesting that partitioning into lipids controls the toxicity.     

Differences in reproductive success between laboratory and wild-derived golden hamsters (Mesocricetus auratus) as a consequence of inbreeding

All laboratory golden hamsters (Mesocricetus auratus) originated from a sibling pairing back in 1930. Due to this extreme founder event, domestic golden hamsters are presumed to be one of the most bottlenecked animal populations. Nevertheless, domestic hamsters show no obvious signs of inbreeding depression in commonly used breeding stocks. To explore the existence of potentially masked inbreeding effects, we compared the reproductive success of laboratory (lab) and wild-derived (wild) golden hamsters. We allowed oestrus females to mate consecutively with lab and wild males. The resulting offspring was genotyped using microsatellites to assess paternity. Finally, we compared male reproductive success to genetic variability, sexual behaviour and different sperm characteristics. Both hamster strains exhibited the expected large difference in genetic diversity (H _wild =0.712±0.062 vs H _lab =0.007±0.007. The reproductive success of wild males dramatically exceeded that of lab males (87% of pups were sired by wild males). Sexual behaviour of wild and lab males only varied in the number of long intromissions (intromissions without ejaculation at the end of the mating). No significant differences were observed in relation to mounting, ejaculation and intromission. There were also no apparent differences in sperm motility, velocity and density or testis histology between wild and lab hamsters. We conclude that the reduced reproductive success of lab males represents a hidden inbreeding effect, although its precise physiological cause remains unclear. These results provide first evidence for a major fitness disadvantage in captive golden hamsters.     

An evaluation of two fluorescence screening methods for the determination of chrysene metabolites in fish bile

Two screening methods, synchronous fluorescence spectrometry (SFS) and high performance liquid chromatography with fluorescence detection (HPLC-F), have been evaluated for their suitability in determining chrysene metabolites in fish bile. The optimal wavelength pair, excitation/emission 272/374 nm, for SFS measurements of chrysene metabolites was identified by analysis of bile taken from fish exposed to the pure compound. This analysis revealed in addition some information about the metabolite pattern. However, when bile from fish exposed to complex and environmentally relevant mixtures of polycyclic aromatic hydrocarbons (PAHs) was analysed using these methods, identification of the chrysene metabolites was poor. Analysis of bile taken from fish exposed to single PAHs identified other three- and four-ring aromatics as the main interfering compounds. Both methods were equally able to discriminate between impacted and reference sites by determination of relative concentrations of fluorescent three- and four-ring aromatics.     

北极陆地生态系统、气候及紫外线辐射的历史演变

在末次盛冰期,地球上很多大陆都被大量的冰层所覆盖,一些浅海域的海床露出水面将先前分离的大陆连接起来.尽管存在一些适宜于动植物生长而未被冰层覆盖的地区,但其年平均气温仍比更新世时期低10～13℃.在盏冰期的几千年时间内冰川开始消融,其显著特征是气候在大约18000～11400年以前出现了一系列的波动.气候在更新世度过一个温暖期后,开始了一个缓慢的全面变冷的过程,这导致了一系列为期几百年至几千年的气候波动,例如发生在大约13世纪晚期至19世纪早期的"小冰期".在最近150000年的气候变化过程中,北极的各种生态系统和生物组成在近10000年接近其最低分布范围.大冰期结束时的全球大范围急剧升温导致了许多物种的消失,这使北极地区的生物多样性大大降低.因此,北极生态系统以及大型脊椎动物等北极生物的生存正在受到威胁,尤其是目前以及将来的全球变暖都会进一步给它们带来重大灾难.已有的证据表明,就像更新世早期的情形那样,北极地区的树线很有可能会进一步向北发展,并迅速进入到苔原地区,从而减小苔原带,这就会进一步增加北极地区物种灭绝的可能性.一些物种将很有可能向北扩大它们的领地,并取代该地区原有的物种.在更新世早期,由于北极地区的海平面相对较低,当树线入侵到现在的海岸地区时,苔原带至少能够在北极圈的一部分低地区域生存,而从目前来看,未来的海平面极有可能上升,这将会对北极苔原带和其它无树生态系统的分布施加进一步的限制.很显然,全球现在的气候状况对北极生态系统带来的负面影响超出更新世的任何时期,很有可能是巨大的,尤其是当各种环境变化(例如紫外线B的增加,大气中氮化合物的沉积,重金属和酸污染,放射性污染物,生物栖息地破碎化)共同作用于北极生态系统时的影响也是前所未有之际.