A BIOLOGICAL MODEL FOR DIRECTIONAL SENSING OF SEISMIC VIBRATION

ABSTRACT There are many applications for a compact device that is capable of indicating the direction of propagation of substrate vibration. In order to develop effective devices for this purpose, it can be helpful to examine biological systems that have evolved specialized sensory systems for finding a vibration source. We are studying an insect model of vibration localization that provides an approach to directional vibration sensing over very small spatial scales. The treehopper Umbonia crassicornis communicates using vibrational signals transmitted along plant stems in the form of bending waves. The insect detects these substrate vibrations using sensors in the legs. Because the legs in this small species span a distance along the stem of only 5 mm, the insect is faced with a difficult localization problem: time-of-arrival differences between receptors on different legs are in the microsecond range, and wavelengths are an order of magnitude larger than the insect's own dimensions. To study this system we constructed a simulator that mimics the surface motion of propagating bending waves, then used the simulator to explore directional sensing mechanisms. Using laser vibrometry, we characterized the dynamic response of the insect's body (analogous to a mass on a set of springs) when driven with vibration of the substrate. We found a remarkable mechanical directionality in the response of the insect's body to substrate vibration, in which small time differences are converted to large amplitude differences across the insect's body. Preliminary evidence suggests that directionality results from the interaction of two modes of vibration in the insect's body: one that responds to the spatial gradient of the vibrational signal, and one that responds to the spatial average of the signal over the region sampled. This system generates a marked directionality in the amplitude response of the insect's body while sampling only 5 mm of a vibration gradient. We believe that a directional sensing system based on this insect model has direct applications to localization of other surface waves, such as those propagating along the surface of the ground

Predator hunting mode and host plant quality shape attack-abatement patterns of predation risk in an insect herbivore

Group formation reduces individual predation risk when the proportion of prey taken per predator encounter declines faster than the increase in group encounter rate (a ack-abatement). Despite a ack-abatement being an important component of group formation ecology, several key aspects have not been empirically studied, that is, interactions with the hunting mode of the predator and how these relationships are modi ed by local habitat quality. In 79 cage trials, we examined individual egg predation risk in di erent-sized egg clutches from the blue willow beetle Phratora vulgatissima for two predators with di erent hunting modes (consumption of full group [Orthotylus marginalis] vs. part group [Anthocoris nemorum]). Because these predators also take nutrients from plant sap, we could examine how the quality of alternative food sources (high- vs. low-quality host plant sap) in uenced a ack-abatement pa erns in the presence of di erent hunting strategies. For the O. marginalis predator, individual egg predation risk was largely independent of group size. For A. nemorum, egg predation risk clearly declined with increasing group size. However, approximately one-third of the grouping bene t was lost to an increase in group detectability. There were clear di erences in a ack-abatement pa erns between plants with high- vs. low-quality sap. When O. marginalis was the predator, there was no clear change in a ack-abatement in relation to host plant quality. However, for A. nemorum there was a clear reduction in overall predation risk and a stronger a ack-abatement pa ern with increasing group size when plant sap quality increased. This implies that the relative bene ts of prey grouping behavior for any species might show diurnal or seasonal changes as other aspects of resource/habitat quality change for the focal predator. Modulation of a ack-abatement by bo om-up e ects such as plant-based food resources is yet to be incorporated into general theory, despite the ubiquity of omnivorous predators and with omnivory being important for shaping food webs, ecosystem functions, and in biological control. Thus, ongoing re nement of a ack- abatement theory by focusing on bo om-up vs. top-down processes could have signi cant impacts on many important contemporary elds of study

Cold War : a Transnational Approach to a Global Heritage

Although within living memory, many countries now consider their surviving Cold War architecture as part of their heritage. It can even be a priority for heritage managers given that significant buildings are often suitable for reuse while extensive ‘brownfield’ sites such as airfields can be used for large-scale redevelopment. In a number of countries whose work we refer to here (notably the United Kingdom and elsewhere in Europe), agencies responsible for managing their country’s heritage have approached this priority by creating national inventories of sites and buildings with a view to taking informed decisions on their future. This paper presents the argument that the wider international context of the Cold War provides a more appropriate (or additional, higher-level) framework for such decision making. Such a ‘transnational’ approach would allow the comparison of similar (e.g. European) sites not merely within national borders but across the full extent of their western NATO1 deployment in Europe and North America. Taking this approach would also allow comparison with related sites in countries that formed part of the eastern-bloc Warsaw Pact.2 After outlining some examples of how national agencies have approached their Cold War heritage, this paper presents the four stages of this transnational approach making provision for an improved understanding and management of Cold War heritage sites wherever they occur. With a specific focus on the direct comparison between England and Russia, and also referring to sites surviving elsewhere within the former NATO and Warsaw Pact regions, as well as the United States, we argue that this four-stage approach: provides new understandings of a complex archaeological and architectural record; gives fresh perspectives on significance; and (importantly in a time of geopolitical instability) does so in a spirit of cooperation and friendship

(Im)material Culture : Towards an Archaeology of Cybercrime

Cybercrime is ubiquitous. People now inhabit a digital environment comprising permanent risk, exponential threats, and multiple virtual/physical harms, forming a global community of malefactors and the criminally exploited. The purpose of this paper is two-fold. First, through an archaeological lens, to characterize the new materiality of cybercrime (including its artefacts and architecture alongside digital/virtual manifestations). And second, to explore the potential for new perspectives on cybercrime borne out of this archaeological approach. In short: what is the archaeology of cybercrime and can new understandings emerge from an archaeological perspective? In undertaking this research we also challenge the long-held presumption that non-physical traces cannot be studied archaeologically. It is our contention that they can

The Signaller's Dilemma: A Cost–Benefit Analysis of Public and Private Communication

Understanding the diversity of animal signals requires knowledge of factors which may influence the different stages of communication, from the production of a signal by the sender up to the detection, identification and final decision-making in the receiver. Yet, many studies on signalling systems focus exclusively on the sender, and often ignore the receiver side and the ecological conditions under which signals evolve.We study a neotropical katydid which uses airborne sound for long distance communication, but also an alternative form of private signalling through substrate vibration. We quantified the strength of predation by bats which eavesdrop on the airborne sound signal, by analysing insect remains at roosts of a bat family. Males do not arbitrarily use one or the other channel for communication, but spend more time with private signalling under full moon conditions, when the nocturnal rainforest favours predation by visually hunting predators. Measurements of metabolic CO(2)-production rate indicate that the energy necessary for signalling increases 3-fold in full moon nights when private signalling is favoured. The background noise level for the airborne sound channel can amount to 70 dB SPL, whereas it is low in the vibration channel in the low frequency range of the vibration signal. The active space of the airborne sound signal varies between 22 and 35 meters, contrasting with about 4 meters with the vibration signal transmitted on the insect's favourite roost plant. Signal perception was studied using neurophysiological methods under outdoor conditions, which is more reliable for the private mode of communication.Our results demonstrate the complex effects of ecological conditions, such as predation, nocturnal ambient light levels, and masking noise levels on the performance of receivers in detecting mating signals, and that the net advantage or disadvantage of a mode of communication strongly depends on these conditions

Wing mechanics, vibrational and acoustic communication in a new bush-cricket species of the genus Copiphora (Orthoptera: Tettigoniidae) from Colombia

Male bush-crickets produce acoustic signals by wing stridulation to call females. Several species also alternate vibratory signals with acoustic calls for intraspecific communication, a way to reduce risk of detection by eavesdropping predators. Both modes of communication have been documented mostly in neotropical species, for example in the genus Copiphora. In this article, we studied vibratory and acoustic signals and the biophysics of wing resonance in C. vigorosa, a new species from the rainforest of Colombia. Different from other Copiphora species in which the acoustic signals have been properly documented as pure tones, C. vigorosa males produce a complex modulated broadband call peaking at ca. 30 kHz. Such a broadband spectrum results from several wing resonances activated simultaneously during stridulation. Since males of this species do rarely sing, we also report that substratum vibrations have been adopted in this species as a persistent communication channel. Wing resonances and substratum vibrations were measured using a μ-scanning Laser Doppler Vibrometry. We found that the stridulatory areas of both wings exhibit a relatively broad-frequency response and the combined vibration outputs fits with the calling song spectrum breadth. Under laboratory conditions the calling song duty cycle is very low and males spend more time tremulating than singing

A ‘Baby GDA’: Norwich’s Airspace during the Second World War

Throughout the Second World War, the Luftwaffe attacked Norwich on various occasions. The impact this had on the city was recorded visually on the ‘Norwich Bomb Map’. This cartographic depiction, however, only records a single ‘horizontal’ component of the aerial ‘battlescape’. In reality, the aerial battlefield comprised a combination of Norwich’s air defences and the flightpaths of the Luftwaffe bombers, which existed in three-dimensional space. As other scholars have developed methodologies for reconstructing anti-aircraft ‘fire domes’, this article will combine these concepts with a new approach that reconstructs historic flightpaths to give a three-dimensional overview of Norwich’s ‘Gun Defended Area’. By examining all components of Norwich’s airspace, this article will demonstrate the importance of considering the vertical component of a battlescape