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Dynamic behavior and damping capacity of auxetic foam pads
A novel set of auxetic (negative Poisson's ratio) open cell polyurethane foam has been developed and tested under dynamic
loading conditions to assess the viscoelastic response under white noise random excitation and compressive cycling. Foam pads
normalized to standard ISO 13753 have been tested at room temperature and frequency bandwidth 10-500 Hz to assess
transmissibility characteristics for possible antivibration glove applications. The results show that the ISO 13753 normalized
transmissibility for these foams falls below 0.6 above 100 Hz, with lower peak maximum stresses under indentation compared to
conventional open cell solids. These results suggest possible use of the auxetic foam for pads or linens against « white fingers«
vibration applications. Further tests have been conducted on cyclic compressive loading up to 3 Hz and loading ratios of 0.95 for
loading histories up to 100000 cycles. The damping capacity of the auxetic foams showed and increase by a factor 10 compared
to the conventional foams used to manufacture the negative Poisson's ratio ones, and stiffness degradation stabilized after few tens on cycles
Lighting as a Circadian Rhythm-Entraining and Alertness-Enhancing Stimulus in the Submarine Environment
The human brain can only accommodate a circadian rhythm that closely follows 24 hours. Thus, for a work schedule to meet the brainâs hard-wired requirement, it must employ a 24 hour-based program. However, the 6 hours on, 12 hours off (6/12) submarine watchstanding schedule creates an 18-hour âdayâ that Submariners must follow. Clearly, the 6/12 schedule categorically fails to meet the brainâs operational design, and no schedule other than one tuned to the brainâs 24 hour rhythm can optimize performance. Providing Submariners with a 24 hour-based watchstanding scheduleâcombined with effective circadian entrainment techniques using carefully-timed exposure to lightâwould allow crewmembers to work at the peak of their daily performance cycle and acquire more restorative sleep. In the submarine environment, where access to natural light is absent, electric lighting can play an important role in actively entrainingâand closely maintainingâcircadian regulation. Another area that is likely to have particular importance in the submarine environment is the potential effect of light to help restore or maintain alertness
Time-Dependent Symmetries of Variable-Coefficient Evolution Equations and Graded Lie Algebras
Polynomial-in-time dependent symmetries are analysed for polynomial-in-time
dependent evolution equations. Graded Lie algebras, especially Virasoro
algebras, are used to construct nonlinear variable-coefficient evolution
equations, both in 1+1 dimensions and in 2+1 dimensions, which possess
higher-degree polynomial-in-time dependent symmetries. The theory also provides
a kind of new realisation of graded Lie algebras. Some illustrative examples
are given.Comment: 11 pages, latex, to appear in J. Phys. A: Math. Ge
Semiflexible Filamentous Composites
Inspired by the ubiquity of composite filamentous networks in nature we
investigate models of biopolymer networks that consist of interconnected floppy
and stiff filaments. Numerical simulations carried out in three dimensions
allow us to explore the microscopic partitioning of stresses and strains
between the stiff and floppy fractions c_s and c_f, and reveal a non-trivial
relationship between the mechanical behavior and the relative fraction of stiff
polymer: when there are few stiff polymers, non-percolated stiff ``inclusions``
are protected from large deformations by an encompassing floppy matrix, while
at higher fractions of stiff material the stiff network is independently
percolated and dominates the mechanical response.Comment: Phys. Rev. Lett, to appear (4 pages, 2 figures
Low Gain Avalanche Detectors (LGAD) for particle physics and synchrotron applications
A new avalanche silicon detector concept is introduced with a low gain in the region of ten, known as a Low Gain Avalanche Detector, LGAD. The detector's characteristics are simulated via a full process simulation to obtain the required doping profiles which demonstrate the desired operational characteristics of high breakdown voltage (500 V) and a gain of 10 at 200 V reverse bias for X-ray detection. The first low gain avalanche detectors fabricated by Micron Semiconductor Ltd are presented. The doping profiles of the multiplication junctions were measured with SIMS and reproduced by simulating the full fabrication process which enabled further development of the manufacturing process. The detectors are 300 ÎŒm thick p-type silicon with a resistivity of 8.5 kΩcm, which fully depletes at 116 V. The current characteristics are presented and demonstrate breakdown voltages in excess of 500 V and a current density of 40 to 100 nAcmâ2 before breakdown measured at 20oC. The gain of the LGAD has been measured with a red laser (660 nm) and shown to be between 9 and 12 for an external bias voltage range from 150 V to 300 V
Electron Beam Nano-Etching in Oxides, Fluorides, Metals and Semiconductors
Etching, lithography, hole formation, surface restructuring and external machining can all be performed on a nanometre scale using an intense electron beam. Results are presented for a range of different materials which demonstrate the variety of mechanisms by which electron beam nano-etching can occur. For example, in crystalline 13-alumina hole formation occurs by surface indentations growing inwards to join up and form a nanometre diameter hole. In amorphous alumina, on the other hand, hole formation is from the inside-out: oxygen gas bubbles form under the electron beam, coalesce, and burst to leave a well defined nanometre diameter hole. In MgO and Si, holes develop from the electron exit surface: whereas in Al voids form along the irradiated volume, leading eventually to the development of a hole at the electron entrance surface. The potential of electron beam nano-etching to lithography and information storage is demonstrated by showing that the entire contents of the Encyclopaedia Britannica can be written on a pinhead
Diverse supramolecular structures formed by self-assembling proteins of the B acillus subtilis spore coat
Bacterial spores (endospores), such as those of the pathogens Clostridium difficile and Bacillus anthracis, are uniquely stable cell forms, highly resistant to harsh environmental insults. Bacillus subtilis is the best studied spore-former and we have used it to address the question of how the spore coat is assembled from multiple components to form a robust, protective superstructure. B.âsubtilis coat proteins (CotY, CotE, CotV and CotW) expressed in Escherichia coli can arrange intracellularly into highly stable macro-structures through processes of self-assembly. Using electron microscopy, we demonstrate the capacity of these proteins to generate ordered one-dimensional fibres, two-dimensional sheets and three-dimensional stacks. In one case (CotY), the high degree of order favours strong, cooperative intracellular disulfide cross-linking. Assemblies of this kind could form exquisitely adapted building blocks for higher-order assembly across all spore-formers. These physically robust arrayed units could also have novel applications in nano-biotechnology processes
Artificial light at night causes conflicting behavioural and morphological defence responses in a marine isopod
This is the final version. Available on open access from the Royal Society via the DOI in this record.âŻData accessibility. Data and R code are included as electronic supplementary
materialEncroachment of artificial light at night (ALAN) into natural habitats is increasingly recognized as a major source of anthropogenic disturbance. Research focussed on variation in the intensity and spectrum of ALAN emissions has established physiological, behavioural and population-level effects across plants and animals. However, little attention has been paid to the structural aspect of this light, nor how combined morphological and behavioural anti-predator adaptations are affected. We investigated how lighting structure, background reflectance and the three-dimensional properties of the environment combined to affect anti-predator defences in the marine isopod Ligia oceanica. Experimental trials monitored behavioural responses including movement and background choice, and also colour change, a widespread morphological anti-predator mechanism little considered in relation to ALAN exposure. We found that behavioural responses of isopods to ALAN were consistent with classic risk-aversion strategies, being particularly exaggerated under diffuse lighting. However, this behaviour was disconnected from optimal morphological strategies, as diffuse light caused isopods to become lighter coloured while seeking out darker backgrounds. Our work highlights the potential for the structure of natural and artificial light to play a key role in behavioural and morphological processes likely to affect anti-predator adaptations, survival, and ultimately wider ecological effects.Natural Environment Research Council (NERC
âSilence does not sound the same for everyoneâ: student teachersâ narratives:Student Teachersâ Narratives Around Behavior Management in Scottish Schools
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