Search

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2007.09.006 Byline: John M.C. Hutchinson, Andreas Wilke, Peter M. Todd Abstract: We used a computer game to examine three aspects of patch-leaving decisions in humans: how well do humans perform compared to the optimal policy, can they adjust their behaviour adaptively in response to different distributions of prey across patches and on what cues are their decisions based? Subjects earned money by catching fish when they briefly appeared within a pond; the timing of appearances was stochastic but at a rate proportional to how many fish remained. Caught fish were not replaced and ponds varied in how many fish they initially contained (according to three different distributions). At any point subjects could move to a new pond, but travel took some time. They delayed this switch much too long. Furthermore, regardless of the distribution of prey, subjects spent longer at ponds where they had found more items (contrary to optimality predictions in two of the environments). However, they apparently responded not to the number of captures directly (despite this appearing on screen) but to the current interval without a capture, to the interval preceding the last capture, and to the time spent at the current pond. Self-reports supported this order of cue importance. Subjects often left directly after a capture, perhaps an example of the Concorde fallacy. High success rate in the preceding patch decreased residence time and subjects appeared to be learning to leave earlier over the latter two thirds of the experiment. Minimization of delay to the next capture alone might explain some of the suboptimal behaviour observed. Author Affiliation: (a) Max Planck Institute for Human Development, Berlin, Germany (a ) Department of Anthropology, University of California, Los Angeles, U.S.A. (a ) School of Informatics and Cognitive Science Program, Indiana University, U.S.A. Article History: Received 16 February 2007; Revised 30 March 2007; Accepted 11 September 2007 Article Note: (miscellaneous) MS. number: 9270R

An analysis of the song routine of the male bird to attract females reveals that too much time spent in singing results in starvation, as the male divides his time between singing and feeding. The female's response to the songs depends on the time of the day. The female discriminates between high quality and low quality male by demanding harder task from a male and by using choice rules based on song output.

The elastic buckling of shell structures such as spherical shells subject to external pressure and cylindrical shells loaded in axial compression is highly sensitive to imperfections and often catastrophic. Recent studies of spherical shells have provided accurate quantitative results for the relation between the buckling pressure and the amplitude and shape of geometric imperfections and, additionally, quantitative results for the energy barrier that must be overcome to buckle the shell by extraneous loadings or disturbances when it is loaded to pressures below the buckling pressure. Results for the simultaneous interaction of imperfections and energy barriers for spherical shells under external pressure will be presented. Numerical studies for probing forces illustrate their use in determining the buckling energy barrier, and new experimental results on energy barriers obtained by others by probing spherical shells will be discussed and compared with predictions. It will be argued that while imperfections determine the buckling load of a shell, the energy barrier at loads below the buckling load supplies important additional information about the relative safety or precariousness of the shell to additional disturbances. Results for the energy barrier for perfect and imperfect spherical shells under external pressure provide important insights into the shell's robustness, or lack thereof, at pressures below the buckling pressure. In particular, the energy barrier trends provide critical insights into the low knockdown factor usually employed in establishing the design load of unstiffened spherical and cylindrical shells. These design loads are shown to correlate with conventional predictions provided that imperfection amplitudes scale as the shell radius. [ABSTRACT FROM AUTHOR]

The effect of three different organically modified layered silicate clays (Nanomer I.30E, Cloisite 30B and Nanofil SE 3000) on the exfoliation process and on the thermal properties and nanostructure of cured trifunctional epoxy resin based nanocomposites was studied. Optical microscopy showed that the best and poorest qualities of clay distribution in the epoxy matrix were obtained with Nanofil SE 3000 and Nanomer I.30E, respectively. However, the isothermal differential scanning calorimetry scans show that, of the three systems, it is only the Nanomer clay that promotes intra-gallery reaction due to homopolymerisation, appearing as an initial rapid peak prior to the cross-linking reaction. This rapid intra-gallery reaction is not present in the curing curve for the Cloisite and Nanofil systems. This fact implies that the fully cured nanostructure of the Cloisite and Nanofil system is poorly exfoliated, which is confirmed by small angle X-ray scattering which shows a scattering peak for these systems at around 2.53°, corresponding to about 3.5 nm d -spacing. [ABSTRACT FROM AUTHOR]

The stability of lightweight space structures composed of longitudinal thin-shell elements connected transversely by thin rods is investigated, extending recent work on the stability of cylindrical and spherical shells. The role of localization in the buckling of these structures is investigated and early transitions into the post-buckling regime are unveiled using a probe that locally displaces the structure. Multiple probe locations are studied and the probe force versus probe displacement curves are analyzed and plotted to assess the structure's stability. The probing method enables the computation of the energy input needed to transition early into a post-buckling state, which is central to determining the critical buckling mechanism for the structure. A stability landscape is finally plotted for the critical buckling mechanism. It gives insight into the post-buckling stability of the structure and the existence of localized post-buckling states in the close vicinity of the fundamental equilibrium path. [ABSTRACT FROM AUTHOR]

Clamped-clamped compressed wide metal columns with length to thickness ratios such that they undergo plastic buckling are considered. Further, the thickness of the columns is assumed to be in the range of microns to tens of microns, typical of elements comprising some of the small-scale lattice materials currently being produced. The strengthening effects associated with plastic strain gradients are expected to influence buckling behavior, and the columns are analyzed using several versions of the available strain gradient plasticity theories. The columns are assumed to be infinitely wide and subject to plane strain deformations. Approximate one-dimensional and exact two-dimensional analyses are presented. The primary focus is the onset of plastic buckling as predicted by bifurcation from the state of uniform compression. However, a numerical post-buckling study is carried out for one class of strain gradient theories for columns with initial imperfections to ascertain if the buckling predictions stemming from this class of theory are realistic. The paper highlights the fact that one class of strain gradient theories does not appear to be adequate for analyzing plastic buckling. [ABSTRACT FROM AUTHOR]

Abstract: In this article, we attempt to address the relative absence of empirical studies of model driven engineering (MDE) in two different but complementary ways. First, we present an analysis of a large online survey of MDE deployment and experience that provides some rough quantitative measures of MDE practices in industry. Second, we supplement these figures with qualitative data obtained from some semi-structured, in-depth interviews with MDE practitioners, and, in particular, through describing the practices of four commercial organizations as they adopted a model driven engineering approach to their software development practices. Using in-depth semi-structured interviewing, we invited practitioners to reflect on their experiences and selected four to use as exemplars or case studies. In documenting some details of their attempts to deploy model driven practices, we identify a number of factors, in particular the importance of complex organizational, managerial and social factors–as opposed to simple technical factors–that appear to influence the relative success, or failure, of the endeavor. Three of the case study companies describe genuine success in their use of model driven development, but explain that as examples of organizational change management, the successful deployment of model driven engineering appears to require: a progressive and iterative approach; transparent organizational commitment and motivation; integration with existing organizational processes and a clear business focus. [Copyright &y& Elsevier]

Techniques are presented for the empirical testing of stochastic dynamic programming models, using a model of the daily singing routine of birds as the main example. The selection of factors to test or predict is important in order to avoid unnecessary averaging.

The mammalian circadian clock component PERIOD2 (PER2) plays a critical role in circadian rhythm entrainment. Recently, a missense mutation at a putative phosphorylation site in hPER2, Ser-662, was identified in patients that suffer from familial advanced sleep phase syndrome (FASPS). Patients with FASPS display abnormal sleep-wake patterns characterized by a lifelong pattern of sleep onset in the early evening and offset in the early morning. Although the phosphorylation of PER2 is strongly implied from functional studies, it has not been possible to study the site-specific phosphorylation of PER2 on Ser-662, and the biochemical functions of this residue are unclear. Here, we used phosphospecific antibodies to show that PER2 is phosphorylated on Ser-662 and flanking casein kinase (CK) sites in vivo. The phosphorylation of PER2 was carried out by the combined activities of casein kinase 1δ (CK1δ) and casein kinase 1&3x20AC; (CK1&3x20AC;) and was antagonized by protein phosphatase 1. PER2 phosphorylation was rapidly induced in response to circadian entrainment of mammalian cell lines and occurred in both cytosolic and nuclear compartments. Importantly, we found that the pool of Ser-662-phosphorylated PER2 proteins was more stable than the pool of total PER2 molecules, implying that the FASPS phosphorylation cluster antagonizes PER2 degradation. Consistent with this idea, a Ser-662 → Ala mutation that abrogated PER2 phosphorylation significantly reduced its half- life, whereas a phosphomimetic Ser-662 -p Asp substitution led to an elevation in half-life. Our combined findings provide new insights into PER2 regulation and the biochemical basis of FASPS. [ABSTRACT FROM AUTHOR]

Ribosomal protein S6 (rpS6) is a critical component of the 40 S ribosomal subunit that mediates translation initiation at the 5′-m7GpppG cap of mRNA. In response to mitogenic stimuli, rpS6 undergoes ordered C-terminal phosphorylation by p70 S6 kinases and p90 ribosomal S6 kinases on four conserved Ser residues (Ser-235, Ser-236, Ser-240, and Ser-244) whose modification potentiates rpS6 cap binding activity. A fifth site, Ser-247, is also known to be phosphorylated, but its function and regulation are not well characterized. In this study, we employed phospho-specific antibodies to show that Ser-247 is a target of the casein kinase 1 (CK1) family of protein kinases. CK1-dependent phosphorylation of Ser-247 was induced by mitogenic stimuli and required prior phosphorylation of upstream S6 kinase/ribosomal S6 kinase residues. CK1-mediated phosphorylation of Ser-247 also enhanced the phosphorylation of upstream sites, which implies that bidirectional synergy between C-terminal phospho-residues is required to sustain rpS6 phosphorylation. Consistent with this idea, CK1-dependent phosphorylation of rpS6 promotes its association with the mRNA cap-binding complex in vitro. Additionally, we show that protein phosphatase 1 (PP1) antagonizes rpS6 C terminus phosphorylation and cap binding in intact cells. These findings further our understanding of rpS6 phospho-regulation and define a direct link between CK1 and translation initiation [ABSTRACT FROM AUTHOR]

Abstract: Cylindrical shells under uniaxial compression and spherical shells under equi-biaxial compression display the most extreme buckling sensitivity to imperfections. In engineering practice, the reduction of load carrying capacity due to imperfections is usually addressed by use of a knockdown factor to lower the critical buckling stress estimated or computed without accounting for imperfections. For thin elastic cylindrical shells under uniaxial compression and spherical shells under equi-biaxial compression, the knockdown factor is typically as small as 0.2. This paper explores the alleviation of imperfection-sensitivity for loadings with a reduced circumferential (transverse) membrane stress component. The analysis of on the effect of an axisymmetric imperfection on the elastic buckling of a cylindrical shell under uniaxial compression is extended to both cylinders and spheres for loadings that produce general combinations of biaxial membrane stresses. Increases in the knockdown factor due to a reduction of the transverse membrane component are remarkably similar for cylindrical and spherical shells. [Copyright &y& Elsevier]

Abstract: A preliminary theoretical study is carried out of the role of micron-scale patterning on the interface toughness of bonded Cu-to-Cu nanometer-scale films. The work is motivated by the experimental studies of [Tadepalli, R., Turner, K.T., Thompson, C.V., 2008b. Effects of patterning on the interface toughness of wafer-level Cu–Cu bonds. Acta Materialia 56, 438–447; Tadepalli, R., Turner, K.T., Thompson, C.V., 2008c. Mixed-mode interface toughness of wafer-level Cu–Cu bonds using asymmetric chevron test. J. Mech. Phys. Solids 56, 707–718.] wherein 400nm Cu films were deposited in a variety of patterns on Si wafer substrates. Specimens were then produced by bringing the Cu surfaces into contact creating thermo-compression bonds. Interface toughness of these specimens was experimentally measured. The present study focuses on interface patterns comprised of bonded strips, called lines, alternating with lines of unbonded interface, all aligned parallel to the crack front. The interface toughness model employs a cohesive zone to represent separation of the interface and flow theory of plasticity to characterize the Cu films. Remote mode I loading is imposed on the elastic Si substrates. The computational model provides the resistance curve of macroscopic crack driving force versus crack advance as dependent on the work of separation and strength of the interface as well as the pattern geometry and the parameters controlling the plasticity of the Cu films. Plasticity in the Cu films makes a major contribution to the macroscopic interface toughness measured by Tadepalli, Turner and Thompson. Highlighted in this study is the difficulty of accurately representing plastic yielding in the thin films and the challenge of capturing the full range of scales in a computational model. [Copyright &y& Elsevier]

Abstract: Dynamic stretching of bilayer plates comprised of an elastomer layer bonded to a metal layer is studied with emphasis on neck development under plane strain. Neck retardation and multiple necks in the metal layer are promoted by the elastomer layer under quasi-static conditions and also by inertia in the all-metal layer under dynamic stretching. The present study explores the interaction of these two effects under the assumption that ductility is unlimited. The study reveals the roles of the elastomer modulus, the metal strength and the rate of stretching in giving rise to necking retardation. [Copyright &y& Elsevier]

Abstract: Retardation of necking under biaxial stretching of bilayer plates comprised of an elastomer layer bonded to a metal layer is studied. Substantial increases in necking limits and consequent energy absorption can be achieved in metal–elastomer bilayers for both quasi-static and dynamic stretching. The phenomena is tied to the fact that under stretching the incremental modulus of the elastomer remains essentially unchanged, or increases, while the incremental modulus of the metal steadily decreases. The effective incremental modulus of the bilayer decreases with stretching but at a lower rate than the metal itself. Since necking instabilities are associated with an erosion of the incremental modulus, necking in the bilayer is delayed to larger strains. Although the strength of a bilayer having the same mass/area as an all-metal plate is reduced, it can nevertheless absorb more energy than the metal plate if the ratio of the elastomer modulus to metal yield stress is sufficiently large. The first part of the paper derives necking limits and energy absorption capacities for bilayers under quasi-static biaxial stretching. The second part of the paper analyses axisymmetric neck development in clamped circular bilayers subject to impulsive pressure loads. The ability of the bilayer to sustain intense impulses is compared to the performance of metal plates of the same material and total mass. Outstanding issues requiring further study are discussed. [Copyright &y& Elsevier]

Abstract: Recent results on fluid–structure interaction for plates subject to high intensity air shocks are employed to assess the performance of all-metal sandwich plates compared to monolithic solid plates of the same material and mass per area. For a planar shock wave striking the plate, the new results enable the structural analysis to be decoupled from an analysis of shock propagation in the air. The study complements prior work on the role of fluid–structure interaction in the design and assessment of sandwich plates subject to water shocks. Square honeycomb and folded plate core topologies are considered. Fluid–structure interaction enhances the performance of sandwich plates relative to solid plates under intense air shocks, but not as significantly as for water blasts. The paper investigates two methods for applying the loading to the sandwich plate—responses are contrasted for loads applied as a time-dependent pressure history versus imposition of an initial velocity. [Copyright &y& Elsevier]

Abstract: Motivated by a selection of results on the plastic buckling of column members within a sandwich plate core where one face of the sandwich is subject to an intense impulse, the problem addressed is one where lateral buckling takes place simultaneously as a compressive axial wave propagates down the member. The bucklewave problem is modeled as an infinitely long column (or wide plate) which is clamped against lateral deflection at the end where velocity is imposed and has a moving clamped condition coinciding with the front of the plastic compression wave. The model reveals that a column or plate suddenly compressed into the plastic range is dynamically stabilized against lateral buckling for lengths that are significantly longer than the corresponding length at which the member would buckle quasi-statically. This stabilization has significant implications for energy absorption under intense dynamic loading. The analysis method is benchmarked against a simpler, but mathematically analogous problem, for which closed form solutions are available: the dynamics of a guitar string lengthening at constant velocity. [Copyright &y& Elsevier]

Abstract: Survival of a plate against an intense, short duration impulsive loading requires the circumvention of failure modes, including those associated with excessive overall deflection and shear-off at supports and webs. All-metal sandwich plates have distinct advantages over comparable weight monolithic plates, especially for intense water loadings. A recently developed mechanics of dynamically loaded sandwich plates by N. A. Fleck and V. S. Deshpande is extended and modified to address the problem of the minimum weight design of plates of given span that must sustain a uniformly distributed impulsive wave in air or water environments. Requirements for core crushing strength and energy absorption are discussed, as are conditions governing shear-off of the face sheet. Dimensionless parameters governing optimal designs are identified. Specific results are presented for plates with square honeycomb cores outlining trends for the best performance that can be achieved and the optimal distribution of mass between faces and core. Optimally designed sandwich plates can sustain water shocks that are two to three times as large monolithic plates of the same mass and material. The model is used to discuss a number of issues relevant to the design of effective metal sandwich plates, including differing requirements for air and water environments, face sheet shear-off resistance, the role of core strength, and the relation between small-scale tests and full-scale behavior. [Copyright &y& Elsevier]

The performance of metal sandwich plates under impulsive blast loads is compared to that of solid plates made of the same material and having the same weight. Three core geometries are considered: pyramidal truss, square honeycomb and folded plate. Plates of infinite length and clamped along their sides are subject to uniform impulsive load. The momentum impulse is applied to the face sheet towards the blast in the case of the sandwich plate, while it is distributed uniformly through the thickness of the solid plate. Large impulses are considered that are sufficient to produce lateral plate deflections more than 10% of the plate width. Fracture is not considered; the plates are assumed to have sufficient ductility to be able to sustain the deformations. A limited study of weight optimization is carried out for each of the core types with respect to the respective geometric parameters, including core and face sheet thickness, core member aspect ratios and relative density. A well-designed sandwich plate can sustain significantly larger blast impulses than a solid plate of the same weight. If the blast medium is water, fluid–structure interaction can reduce the momentum imparted to a sandwich plate by almost a factor of two relative to that imparted to a solid plate of the same weight, and, consequently, the relative benefit of the sandwich plate is significantly enhanced over its solid counterpart. [Copyright &y& Elsevier]

Sandwich plates with truss cores fashioned from straight struts have distinct advantages relative to other constructions, including those with honeycomb cores. In addition to opportunities afforded by their open architecture, the truss core sandwich plates meet or exceed the load carrying capacity of other competitive constructions. The weight of truss core sandwich plates subject to a crushing stress and arbitrary combinations of bending and transverse shear are optimized subject to buckling and plastic yielding constraints and then compared with the weight performance of other types of optimized plates. Several issues central to the optimization process are addressed by a fundamental model study. These include the relation of designs based on a pure moment loading to those based on combined moment and transverse shear and the accuracy needed to model the various modes of buckling that must be taken into account in the design process. [Copyright &y& Elsevier]

Upon cooling, a thin metal film deposited on compliant elastomer substrate undergoes equi-biaxial compression and begins to buckle at a critical stress. As further cooling occurs, a highly ordered herringbone pattern self-assembles. The preference for the herringbone pattern over other potential modes is demonstrated based on minimum energy arguments. Control of the pre-buckling in-plane stress components may be one way to influence the pattern formation, possibly giving rise to a family of unbalanced herringbone modes that links one-dimensional modes with the balanced herringbone mode. [Copyright &y& Elsevier]

The phenomena governing the durability of thermal barrier coatings (TBCs) are affected by their high temperature mechanical properties: especially the mechanisms of material removal upon particle impact. Some high temperature properties can be explored using an impression test described in a companion article. The utility of the test is contingent upon a method for deconvoluting aspects of the stress/strain response from load–displacement measurements. A numerical procedure having this attribute is described, and applied to TBCs with a columnar microstructure. The method elucidates the extent of the plastic deformation and densification as well as the column distortions caused by the impression. It is also capable of exploring the deformation heterogeneities observed experimentally, such as shear bands, by embodying salient constituent properties, such as the column width, contact friction, and inter-columnar friction. Comparisons with measurements provide some understanding of the plastic response of several thermal barrier systems. [Copyright &y& Elsevier]

By way of numerical examples, this paper explores the nature of solutions to a class of strain gradient plasticity theories that employ conventional stresses, equilibrium equations and boundary conditions. Strain gradients come into play in these modified conventional theories only to alter the tangent moduli governing increments of stress and strain. It is shown that the modification is far from benign from a mathematical standpoint, changing the qualitative character of solutions and leading to a new type of localization that is at odds with what is expected from a strain gradient theory. The findings raise questions about the physical acceptability of this class of strain gradient theories. [Copyright &y& Elsevier]

The question motivating the present study is whether metal sandwich plates with sufficiently strong cores are able to sustain substantially larger blast loads than monolithic solid plates of the same material and total mass. Circular plates clamped at their edges are considered under blast loads large enough to produce substantial deflections. The material is elastic–perfectly plastic. Material strain-rate dependence and fracture are neglected. A dynamic finite element formulation for elastic–plastic solids is employed to analyze the plate response. Uniformly distributed blast impulses are considered. As a basis for comparison, complete results are obtained for solid plates for both zero-period and finite-period impulses. Similar computations are carried out for a set of sandwich plates having tetragonal truss cores. The potential for superior strength and energy absorbing capacity of the sandwich plates is demonstrated compared with solid plates having the same mass. The importance of both the strength and energy absorbing capacity of the core are highlighted for superior blast resistance. Proposals for further research are made. [Copyright &y& Elsevier]

The anatomy and functions of muscle–tendon complexes and their bony attachments in birds and their outgroups show how the major pelvic limb muscle groups evolved. Fossils reveal that most changes evolved after the divergence of archosaurs in the Triassic, particularly in the dinosaurian precursors to birds. Three-dimensional limb control became concentrated at the hip joint; more distal joints and muscles were restricted to flexion or extension early in dinosaur evolution. Hip extensors expanded even though the primary femoral retractor M. caudofemoralis longus was reduced. Hip flexors and two-joint ‘hamstring’ muscles were simplified to a few large heads. Knee extensors increased their sizes and moment arms early in bipedal dinosaurs, but the patella and cranial cnemial crest evolved later in birds. Lower limb muscles expanded as ossifications such as the hypotarsus increased their moment arms. The ossification of lower limb tendons, particularly in extensors, is a recent novelty of birds. Muscles and tendons that develop large forces, stresses, and moments to stabilize or move the limbs became increasingly prominent on the line to birds. Locomotion evolved in a stepwise pattern that only recently produced the derived limb control mechanisms of crown-group birds, such as the strongly flexed hip and knee joints. [Copyright &y& Elsevier]

Background: Noninvasive imaging autopsy alternatives for fetuses weighing <500 grams are limited. Microfocus computed tomography has been reported as a viable option in small case series with the potential to avoid an invasive autopsy. Implementation of postmortem microfocus computed tomography in a large cohort as part of routine clinical service has yet been unreported, and realistic "autopsy prevention rates" are unknown.Objective: This study aimed to describe the range of abnormalities detectable on fetal microfocus computed tomography in a clinical setting and additional findings identified on the antenatal ultrasound and to estimate the invasive autopsy avoidance rate (ie, cases in which imaging was sufficient to deem autopsy unnecessary).Study Design: A prospective observational case series of all fetuses referred for microfocus computed tomography imaging at a single institution was conducted for 3 years (2016-2019). Imaging was reported by 2 pediatric radiologists before autopsy, with "decision to proceed" based on the specialist perinatal pathologists' judgment and parental consent. Agreement rates between microfocus computed tomography and antenatal ultrasound were evaluated, and where feasible, diagnostic accuracy for microfocus computed tomography was calculated using autopsy as a reference standard.Results: A total of 268 fetuses were included (2-350 grams body weight; 11-24 weeks' gestation), with cause for demise in 122 of 268 (45.5%). Of the 122 fetuses, 64 (52.5%) exhibited fetal anomalies. Although 221 of 268 (82.5%) fetuses had consent for invasive autopsy, only 29 of the 221 (13.1%) underwent this procedure, which implied an autopsy avoidance rate of 192 of 221 (86.9%). Complete agreement was present for all brain, thoracic, and abdominal pathologies, whereas sensitivity and specificity for cardiac anomalies were 66.7% and 91.7%, respectively. Microfocus computed tomography and antenatal ultrasound agreement was found in 219 of 266 cases (81.9%), with partial agreement in 21 of 266 (7.9%) and disagreement in 26 of 266 (10.5%), mostly because of additional cardiac, soft tissue, or genitourinary findings by microfocus computed tomography, which were not seen on the ultrasound.Conclusion: Fetal microfocus computed tomography imaging is a viable and useful tool for imaging early gestational fetuses and can avoid the need for invasive autopsy. Confirmation of antenatal diagnoses is achieved in most cases, and additional anomalies may also be detected. [ABSTRACT FROM AUTHOR]

Single-loop elastic rings can be folded into multi-loop equilibrium configurations. In this paper, the stability of several such multi-loop states which are either circular or straight are investigated analytically and illustrated by experimental demonstrations. The analysis ascertains stability by exploring variations of the elastic energy of the rings for admissible deformations in the vicinity of the equilibrium state. The approach employed is the conventional stability analysis for elastic conservative systems based on the second variation of the system energy which differs from most of the analyses that have been published on this class of problems, as will be illustrated by reproducing and elaborating on several problems in the literature. In addition to providing solutions to two basic problems, the paper analyses and demonstrates the stability of six-sided rings, curved-sided hexagrams, that fold into straight configurations. [ABSTRACT FROM AUTHOR]

Background: Perinatal autopsy provides useful clinical information in up to 40% of cases. However, there is a substantial unmet clinical need with regards to postmortem investigation of early gestation fetal loss for parents for whom standard autopsy is either not available or not acceptable. Parents dislike the invasive nature of autopsy, but current clinical imaging techniques do not provide high-enough imaging resolution in small fetuses. We hypothesized that microfocus computed tomography, which is a rapid high-resolution imaging technique, could give accurate diagnostic imaging after early gestation fetal loss.Objective: The objective of the study was to evaluate the diagnostic accuracy of microfocus computed tomography for noninvasive human fetal autopsy for early gestation fetuses, with the use of conventional autopsy as the reference standard.Study Design: We compared iodinated whole body microfocus computed tomography in 20 prospectively recruited fetuses (11-21 weeks gestation from 2 centers) with conventional autopsy in a double-blinded manner for a main diagnosis and findings in specific body organs. Fetuses were prepared with 10% formalin/potassium tri-iodide. Images were acquired with a microfocus computed tomography scanner with size-appropriate parameters. Images were evaluated independently by 2 pediatric radiologists, who were blinded to formal perinatal autopsy results, across 40 individual indices to reach consensus. The primary outcome was agreement between microfocus computed tomography and conventional autopsy for overall diagnosis.Results: Postmortem whole body fetal microfocus computed tomography gave noninvasive autopsy in minutes, at a mean resolution of 27μm, with high diagnostic accuracy in fetuses at <22 weeks gestation. Autopsy demonstrated that 13 of 20 fetuses had structural abnormalities, 12 of which were also identified by microfocus computed tomography (92.3%). Overall, microfocus computed tomography agreed with overall autopsy findings in 35 of 38 diagnoses (15 true positive, 18 true negative; sensitivity 93.8% [95% confidence interval, 71.7-98.9%], specificity 100% [95% confidence interval, 82.4-100%]), with 100% agreement for body imaging diagnoses. Furthermore, after removal of nondiagnostic indices, there was agreement for 700 of 718 individual body organ indices that were assessed on microfocus computed tomography and autopsy (agreement, 97.5%; 95% confidence interval, 96.1-98.4%), with no overall differences between fetuses at ≤14 or >14 weeks gestation (agreement, 97.2% and 97.9%, respectively). Within first-trimester fetal loss cases (<14 weeks gestation), microfocus computed tomography analysis yielded significantly fewer nondiagnostic indices than autopsy examination (22/440 vs 48/348, respectively; P<.001).Conclusion: Postmortem whole-body fetal microfocus computed tomography gives noninvasive, detailed anatomic examinations that are achieved in minutes at high resolution. Microfocus computed tomography may be preferable to magnetic resonance imaging in early gestation fetuses and may offer an acceptable method of examination after fetal loss for parents who decline invasive autopsy. This will facilitate autopsy and subsequent discussions between medical professionals who are involved in patient care and counselling for future pregnancies. [ABSTRACT FROM AUTHOR]

Abstract Objective To describe the anaesthetic, physiological and side effects of intramuscular (IM) medetomidine and ketamine, followed by inhalational anaesthesia with sevoflurane, in Nile crocodiles (Crocodylus niloticus). Study design Observational trial. Animals Ten juvenile captive-bred Nile crocodiles undergoing surgical implantation of skeletal beads and muscular electrodes. Methods During preanaesthetic examination, the following variables were assessed: heart (HR) and respiratory (f R) rates, and response to palpebral, corneal and toe- and tail-pinch withdrawal reflexes. The crocodiles were injected IM with an initial combination of medetomidine and ketamine and re-evaluated at 5 minute intervals for 20 minutes, or until they appeared unresponsive. If that did not occur, the drugs were redosed according to a decision tree based on the observed effects. The righting, biting and palatal valve reflexes were assessed in the unresponsive crocodiles, and used to confirm anaesthetic induction. Anaesthesia was maintained with sevoflurane in oxygen. At the end of surgery, medetomidine was antagonized with IM atipamezole. Results The decision tree identified 0.3 mg kg−1 medetomidine and 15 mg kg−1 ketamine as a useful drug combination, which resulted in anaesthetic induction and surgical anaesthesia 16 ± 8 and 16 (25–20) minutes after injection, respectively. Compared to baseline, HR and f R significantly decreased after anaesthetic induction (p < 0.001), but then remained stable throughout surgery. Intraoperatively, cloacal temperature [27 (26–30) °C] did not change over time (p = 0.48). The total dose of atipamezole was 2 (1–3) mg kg−1 and time to recovery was 36 (20–60) minutes. Perioperative complications were not observed. Conclusions and clinical relevance Medetomidine and ketamine, injected IM and followed by sevoflurane anaesthesia, may be regarded as a useful anaesthetic technique for juvenile Nile crocodiles undergoing minimally invasive experimental surgery. [ABSTRACT FROM AUTHOR]