The goal of this article is to complement the comprehensive account Spatial Vision in Arthorpods provided by Wehner R. (1981) in the Handbook of Sensory Physiology. We will confine ourselves to review a selection of examples where over the last decades an integrated approach of quantitative behavioral studies in combination with electrophysiology and modeling best illustrates neural mechanisms underlying visually guided behavior. Many of these studies have been successfully carried out in a variety of flying insects, namely flies.

Recent advances in the description of fibre-reinforced polymer composite material behaviour under extreme loading rates provide a significant extension in capabilities for numerical simulation of hypervelocity impact on composite satellite structures. Given the complexity of the material model, extensive material characterisation is required, however, as the properties of composite materials are commonly tailored for a specific application, experimental characterisation is not efficient, particularly in preliminary design phases. As such, a procedure is outlined in this paper that applies a number of commonly accepted composite mechanics and shock physics theories in conjunction with generalised material properties which allows for the theoretical derivation of a complete material data set for utilisation of the new modelling capabilities. The derivation procedure has been applied to a carbon fibre/epoxy laminate, and is validated through a comparison of derived material properties with experimentally characterised values and numerical simulation of damage induced by hypervelocity impact on a representative space debris shielding configuration employing the CFRP laminate. For the specific structures and impact conditions considered, application of the material property derivation procedure in place of experimental characterisation provided comparable accuracy in the prediction of damage induced by particles impacting at hypervelocity.

The ionomer Surlyn (R) 8940 is known for its ability to self-heal projectile impact damage. In previous studies, the resin was compression molded to obtain polymer sheets that exhibited the expected self-healing behavior. In this study, however, extruded polymer sheets were used. In contrast to the compression molded sheets, the extruded ones were not able to self-heal the impact damage. In order to clarify this change in self-healing behavior caused by the two different manufacturing processes, the compression molded and extruded materials were further investigated by tensile tests and differential scanning calorimetry (DSC). Furthermore, finite element simulations were done and compared with the experimental results.

Due to their low weight and high stiffness, sandwiches consisting of CFRP face sheets and aluminium honeycomb cores are widely used in aerospace structures. Considering threats like foreign object debris for aircraft or space debris for spacecraft, it is important to understand the effects of impact events on such lightweight structures. This paper gives an overview of the derivation and validation of a numerical material model that predicts the highly dynamic behaviour of CFRP under HVI (hypervelocity impact).

This paper describes the derivation and validation of a numerical material model that predicts the highly dynamic behaviour of CFRP (carbon fibre reinforced plastic) under hypervelocity impact. CFRP is widely used in satellites as face sheet material in CFRP-Al/HC sandwich structures (HC = honeycomb) that can be exposed to space debris. A review of CFRP-Al/HC structures typically used in space was performed. Based on this review, a representative structure in terms of materials and geometry was selected for study in the work described here. An experimental procedure for the characterisation of composite materials is documented by Riedel et al. [ADAMMO - advanced material damage models for numerical simulation codes. ESA CR(P) 4397, EMI report 175/03, Freiburg: October 31, 2003.]. The test results from the CFRP of the current study allow for the derivation of an experimentally based orthotropic continuum material model data set that is capable of predicting the mechanical behaviour of CFRP under hypervelocity impact. Such a data set was not previously available. In the work by Riedel et al. [Hypervelocity impact damage prediction in composites: part II - experimental investigations and simulations. International journal of Impact Engineering, 2006:33:670-80.] an orthotropic material data set was used for modelling HVI on AFRP (aramid fibre reinforced plastic), which shows relatively high deformability before failure. The enhancements of the modelling approaches in previous studies [Riedel W, Harwick W, White DM, Clegg RA. ADAMMO - advanced material damage models for numerical simulation codes. ESA CR(P) 4397, EMI report I 75/03, Freiburg: October 31, 2003. Hiermaier S, Riedel W, Hayhurst C, Clegg RA, Wentzel C. AMMHIS - advanced material models for hypervelocity impact simulations. Final report, EMI report E 43/98, ESA CR(P) 4305, Freiburg: July 30,1999.] necessary to model brittle CFRP are specified. An experimental hypervelocity impact campaign was performed at two different two-stage light gas guns which encompassed both normal and oblique impacts for a range of impact velocities and projectile diameters. Validation of the numerical model is provided through comparison with the experimental results. For that purpose measurements of the visible damage of the face sheets and of the HC core are conducted. In addition, the numerically predicted damage within the CFRP is compared to the delamination areas found in ultrasonic scans. (C) 2008 Elsevier Ltd. All rights reserved.

MLI (multi-layer insulation) is present in many spacecraft missions and typically consists of multiple layers of aluminized Kapton separated by fine gauze. It has been observed, depending on the type and position within the structure, that MLI can influence the ballistic performance of panels under hypervelocity impact (HVI) despite being extremely lightweight. Due to the very thin nature of the foils, <10μm, it is often considered too computationally expensive to explicitly include such materials in HVI simulations of typical structures used in space. Accurate resolution of the foils would require a prohibitive number of elements. This paper reports on the development of a discrete modelling approach that efficiently facilitates the inclusion of such materials and allows for each layer of the MLI to be explicitly represented in the numerical model. Mesomechanical simulations of planar plate impact experiments (PPI) and an HVI event on MLI are presented where each layer of the MLI is explicitly represented with a number of elements through the thickness. The results of these models are then compared with the developed discrete approach suitable for including in larger scale simulations of impacts on real space structures. The current study applies previously developed material models to structural materials such as Carbon Fiber Reinforced Plastics (CFRP). This paper further describes simulation of an HVI event on a CFRP-Aluminum/honeycomb structure at oblique incidence, thereby illustrating that the developed approach for modelling MLI provides a practical method for the inclusion of such materials in full-scale simulations.

Manned space missions demand advanced safety requirements concerning protection against space debris and meteoroid impacts which lead to heavy shielding structures. In order to decrease the weight of shield systems without compromising the protection performance, or in order to increase protection levels at constant weight, modem shield concepts have been evaluated by means of experimental and numerical impact simulations. New configurations have been compared with existing "Stuffed Whipple Shield" protection systems. Such systems consist of an Al-bumper and a so-called "stuffing layer" consisting of a combination of ceramic and aramid fabrics. Results are presented for Al-foam sandwich bumpers and bumpers of TiAl super alloys. A number of materials have been implemented as stuffing layers: Kevlar fabrics, Nextel fabrics combined with Kevlar fabrics, and Kevlar fabrics combined with polyurethane foam. Numerical simulations are carried out for the Al-foam shields. These calculations are conducted mesomechanically, i.e. the cell walls of the foam are modelled explicitly with a finite element mesh. The aim is to study the influence of the foam on the distribution of momentum of the debris cloud.

The elastic and plastic behaviour of an open-cell aluminium foam is investigated numerically. Finite element discretisations are used that have been derived from real foam specimens by computer tomography data. By different combinations of boundary velocities in the three directions in space, various multiaxial stress states are realised in the foam. This is done for nine foam discretisations with varying relative density. Thus, the elastic constants, the yield surface and the plastic potential of the foam are determined depending on the relative density. The results of the numerical simulations are: (1) the variation of the Young's modulus in terms of the relative density can be described by a power law relationship. (2) The elastic Poisson's ratio does not depend on the relative density. (3) The yield surface is not rotationally symmetric with regard to the hydrostatic axis. (4) The dimensions of the yield surface vary with a power law relationship in terms of the relative density. (5) The plastic potential is approximately associated to the yield surface for all stress states.

Amorphous hydrogenated silicon (a-Si:H) films in the thickness range 0.1–4.5 nm were deposited on Si(100) surfaces at 350 K using the ion-beam-deposition method. The thermal stability of these a-Si:H films was studied by temperature programmed desorption spectroscopy. The films are stable up to 500 K, where a-Si:H starts to decompose via evolution of hydrogen (H2) and silane (SiH4). Approximately 99% of the hydrogen initially bound to the Si network was detected in the hydrogen channel. The hydrogen evolution peaks at ∼780 K caused by the decomposition of monohydride groups; the presence of SiH2 groups is indicated by hydrogen desorption below 700 K. The silane desorption states at 625 and 750 K reveal the existence of two different types of silyl (SiH3) groups. Etching of a-Si:H by impinging gas-phase H atoms was investigated in the temperature range from 150 to 700 K by in situ mass spectrometry. Silane was the sole etch product observed. The formation of silane proceeds via direct abstraction of silyl precursor groups by impinging hydrogen atoms, SiH3(a)+H(g)→SiH4(g); the silyl abstraction probability increases by a factor of 6 with increasing substrate temperature between 150 and 525 K. However, the steady-state erosion rate is controlled by the supply of silyl groups by successive hydrogenation of the Si network with the formation of SiH2 as bottleneck of the silyl supply.

The formation and the thermal stability of silyl (SiH3) groups on Si(1 0 0) surfaces was investigated by mass spectrometry. Silyl groups were prepared either by adsorption and decomposition of disilane (Si2H6) on clean Si(1 0 0), or by using thermal hydrogen atoms to generate silicon hydride groups. The silyl coverage decreases with increasing temperature during disilane or H atom exposure. Maximum silyl coverages of 0.15 and 0.12 ML, respectively, were obtained after disilane or H atom saturation exposures at 110 K. On saturated Si(1 0 0) surfaces, i.e., in absence of dangling bonds, silyl groups are stable up to 500 K; above 500 K the formation of silane (SiH4) via disproportionation, -SiH3(a) + SiH2(a) --> SiH4(g) + SiH(a), was observed. In the presence of dangling bonds, silyl groups decompose toward SiH, and SiH groups, even at 110 K.The abstraction of adsorbed silyl by impinging hydrogen atoms, -SiH3(a) + H(g) --> SiH4(g), was investigated in the temperature range from 110 to 800 K by in situ mass spectrometry. Silane was the sole product observed. The silyl abstraction probability increases by a factor of 6 with increasing substrate temperature between 110 and 500 K, indicating an apparent activation energy of 12.5 kJ mol(-1), which can be discussed in terms of an increased reaction probability of vibrationally excited silyl groups. The regeneration of silyl groups by impinging hydrogen atoms was identified as the rate limiting step of the hydrogen induced etching of silicon under steady-state conditions. (C) 2001 Elsevier Science B.V. All rights reserved.

Visual perception of depth change can be mediated monocularly by looming the apparent size increase of an approaching object. In Manduca sexta we recorded intracellularly from cells that detect both approach and retreat of an object. The cells compute looming in two fundamentally different ways: class 1 neurons measure the change of perimeter/edge length of the object; class 2 neurons respond to expansion/contraction flowfields. We created a network model incorporating anatomical and physiological properties of class 1 neurons to understand the underlying computational principles for looming detection.

Visual stimuli representing looming or receding objects can be decomposed into four parameters: change in luminance; increase or decrease of area; increase or decrease of object perimeter length; and motion of the object's perimeter or edge. This paper describes intracellular recordings from visual neurons in the optic lobes of Manduca sexta that are selectively activated by certain of these parameters. Two classes of wide-field neurons have been identified that respond selectively to looming and receding stimuli. Class 1 cells respond to parameters of the image other than motion stimuli. They discriminate an approaching or receding disc from an outwardly or inwardly rotating spiral, being activated only by the disc and not by the spiral. Class 2 neurons respond to moving edges. They respond both to movement of the spiral and to an approaching or receding disc. These two classes are further subdivided into neurons that are excited by image expansion (looming) and are inhibited by image contraction (antilooming). Class 2 neurons also respond to horizontal and vertical movement of gratings over the retina. Stimulating class 1 and 2 neurons with white discs against a dark background results in the same activation as stimulation with dark discs against a white background, demonstrating that changes in luminance play no role in the detection of looming or antilooming. The present results show that the two types of looming-sensitive neurons in M. sexta use different mechanisms to detect the approach or retreat of an object. It is proposed that cardinal parameters for this are change of perimeter length detected by class 1 neurons and expansion or contraction visual flow fields detected by class 2 neurons. These two classes also differ with respect to their polarity, the former comprising centripetal cells from the optic lobes to the midbrain, the latter comprising centrifugal neurons from the midbrain to the optic lobes. The significance of these arrangements with respect to hovering flight is discussed. J. Comp. Neurol. 424:356-376, 2000. (C) 2000 Wiley-Liss, Inc.

Summary  Three types of receptor cells responding respectively to the pheromone components (E,Z)-6,11-hexadecadienyl acetate (AC1, (E,Z)-6,11-hexadecadienal (AL) and (E,Z)-4,9-tetradecadienyl acetate (AC2) occur in different combinations in the sensilla trichodea on male antennae ofAntheraea polyphemus andA. pernyi. The numbers of cells sensitive to AC1 and AL and the average sensitivities of these cells are about equal, and higher than those of the AC2-cells. The cells sensitive to AC2 are relatively common in the small hairs positioned on the anterior side of the antenna. The product of three experimental values — (i) the relative number of each cell type, (ii) the average relative sensitivity of the cells and (iii) the estimated relative release rate of the respective pheromone component from the female gland — suggest that the distance from the female over which a compound can be detected or, the potential active space, is different for each pheromone component.