Coriolis and centrifugal forces drive haltere deformations and influence spike timing.

The halteres of flies are mechanosensory organs that serve a crucial role in the control of agile flight, providing sensory input for rapid course corrections to perturbations. Derived from hind wings, halteres are actively flapped and are thus subject to a variety of inertial forces as the fly undergoes complex flight trajectories. Previous analyses of halteres modelled them as a point mass, showing that Coriolis forces lead to subtle deflections orthogonal to the plane of flapping. By design, these models could not consider the effects of force gradients associated with a mass distribution, nor could they reveal three-dimensional spatio-temporal patterns of strain that result from those forces. In addition, diversity in the geometry of halteres, such as shape and asymmetries, could not be simply modelled with a point mass on a massless rod. To study the effects of mass distributions and asymmetries, we examine the haltere subject to both flapping and body rotations using three-dimensional finite-element simulations. We focus on a set of simplified geometries, in which we vary the stalk and bulb shape. We find that haltere mass distribution gives rise to two unreported deformation modes: (i) halteres twist with a magnitude that strongly depends on stalk and bulb geometry and (ii) halteres with an asymmetric mass distribution experience out-of-plane bending due to centrifugal forces, independent of body rotation. Since local strains at the base of the haltere drive deformations of mechanosensory neurons, we combined measured neural encoding mechanisms with our structural analyses to predict the spatial and temporal patterns of neural activity. This activity depends on both the flapping and rotation dynamics, and we show how the timing of neural activity is a viable mechanism for rotation-rate encoding. Our results provide new insights in haltere dynamics and show the viability for timing-based encoding of fly body rotations by halteres.

Induction of skin carcinogenicity by alcohol and ultraviolet light.

In western societies, casual consumption of alcohol during such outdoor activities as barbecuing and sunbathing is common. The current literature shows that alcohol drinkers have increased episodes of sunburn and a higher prevalence of skin cancer. Moreover, recent evidence suggests that the combination of subcarcinogenic (minimal) ultraviolet (UV) exposure with other behavioural, environmental and xenobiotic factors has resulted in increased incidents of skin-related health problems that also result in skin-cancer formation. We hypothesize that the combination of alcohol consumption with UV radiation can potentiate the skin carcinogenic effects through the intermediate biproducts or metabolites of alcohol, which serve as the photosensitizers, consequently enhancing the cellular damage. We have proposed a mechanism that explains the combined alcohol-UV radiation carcinogenicity and its potential involvement in enhancing skin damage in the multistep skin carcinogenesis process. Previous literature has explored this mutual effect but no studies have definitively ascribed the reasons for increased skin cancer prevalence among alcohol drinkers. Nevertheless, the preceding epidemiological data and clinical studies recognize this matter, making the further testing of this hypothesis necessary.

Metabolic demands of rock climbing in transfemoral amputees.

This pilot study compared the energy expenditure required to climb an indoor rock wall, in amputees utilizing five prosthetic configurations. Three experienced climbers (1M age 21 yr, 2F ages 30 and 49 yr) with unilateral transfemoral amputation climbed a 9.14 m indoor rock wall, 5.9 Yosemite Decimal Scale rating, using the following prosthetic configurations: 1. no prosthesis; 2. stubby prosthesis-foot forward; 3. stubby prosthesis-foot backward; 4. articulated prosthesis-knee unlocked; 5. articulated prosthesis-knee locked. Subjects climbed three times with each configuration resulting in 15 climbs per subject. Metabolic data was collected using the COSMED K4b(2) system. VO(2) was 15, 18 and 20% greater in the articulated unlocked condition (mean+/-SE: 20.5+/-0.8 ml.kg (-1).min (-1)), and 11, 13 and 15% greater in the articulated locked condition (19.7+/-0.9 ml.kg (-1).min (-1)), compared to the no prosthesis (17.8+/-0.7 ml.kg (-1).min (-1)), stubby backward (17.4+/-0.7 ml.kg (-1).min (-1)) and stubby forward (17.1+/-0.9 ml.kg (-1).min (-1)) conditions. Participants expended 11-20% more energy using the articulated prostheses than with the stubby and no prosthesis conditions. In persons with transfemoral amputation, use of an articulated prosthesis in indoor rock climbing may be a disadvantage in many aspects including competition, training, rehabilitation and satisfaction with the activity.

A neural basis for gyroscopic force measurement in the halteres of Holorusia.

Dipteran flight requires rapid acquisition of mechanosensory information provided by modified hindwings known as halteres. Halteres experience torques resulting from Coriolis forces that arise during body rotations. Although biomechanical and behavioral data indicate that halteres detect Coriolis forces, there are scant data regarding neural encoding of these or any other forces. Coriolis forces arise on the haltere as it oscillates in one plane while rotating in another, and occur at oscillation frequency and twice the oscillation frequency. Using single-fiber recordings of haltere primary afferent responses to mechanical stimuli, we show that spike rate increases linearly with stimulation frequency up to 150 Hz, much higher than twice the natural oscillation frequency of 40 Hz. Furthermore, spike-timing precision is extremely high throughout the frequency range tested. These characteristics indicate that afferents respond with high speed and high precision, neural features that are useful for detecting Coriolis forces. Additionally, we found that neurons respond preferentially to specific stimulus directions, with most responding more strongly to stimulation in the orthogonal plane. Directional sensitivity, coupled with precise, high-speed encoding, suggests that haltere afferents are capable of providing information about forces occurring at the haltere base, including Coriolis forces.

Prey size selection and distance estimation in foraging adult dragonflies.

To determine whether perching dragonflies visually assess the distance to potential prey items, we presented artificial prey, glass beads suspended from fine wires, to perching dragonflies in the field. We videotaped the responses of freely foraging dragonflies (Libellula luctuosa and Sympetrum vicinum-Odonata, suborder Anisoptera) to beads ranging from 0.5 mm to 8 mm in diameter, recording whether or not the dragonflies took off after the beads, and if so, at what distance. Our results indicated that dragonflies were highly selective for bead size. Furthermore, the smaller Sympetrum preferred beads of smaller size and the larger Libellula preferred larger beads. Each species rejected beads as large or larger than their heads, even when the beads subtended the same visual angles as the smaller, attractive beads. Since bead size cannot be determined without reference to distance, we conclude that dragonflies are able to estimate the distance to potential prey items. The range over which they estimate distance is about 1 m for the larger Libellula and 70 cm for the smaller Sympetrum. The mechanism of distance estimation is unknown, but it probably includes both stereopsis and the motion parallax produced by head movements.

Response to radiation.

Computed tomography (CT) has traditionally been the standard radiographic modality for diagnosing and monitoring non-small cell; lung cancer (NSCLC) after treatment. Given the limitations of CT, the utility of 18F-fluoro-2-deoxy-glucose positron emission tomography (FDG-PET) has been investigated for the management of NSCLC, with promising findings. Its adjunctive role with CT in diagnosing and staging disease is well established. FDG-PET also has been found to be a valuable tool for radiation treatment planning because it improves the precision of lesion definition. More recently, its value for determining clinical response both during and after treatment has been explored. This review highlights the various applications of FDG-PET in the diagnosis and management of NSCLC as corroborated by clinical data, with considerations of future directions.

Genetic characterization of highly fluoroquinolone-resistant clinical Escherichia coli strains from China: role of acrR mutations.

The genetic basis for fluoroquinolone resistance was examined in 30 high-level fluoroquinolone-resistant Escherichia coli clinical isolates from Beijing, China. Each strain also demonstrated resistance to a variety of other antibiotics. PCR sequence analysis of the quinolone resistance-determining region of the topoisomerase genes (gyrA/B, parC) revealed three to five mutations known to be associated with fluoroquinolone resistance. Western blot analysis failed to demonstrate overexpression of MarA, and Northern blot analysis did not detect overexpression of soxS RNA in any of the clinical strains. The AcrA protein of the AcrAB multidrug efflux pump was overexpressed in 19 of 30 strains of E. coli tested, and all 19 strains were tolerant to organic solvents. PCR amplification of the complete acrR (regulator/repressor) gene of eight isolates revealed amino acid changes in four isolates, a 9-bp deletion in another, and a 22-bp duplication in a sixth strain. Complementation with a plasmid-borne wild-type acrR gene reduced the level of AcrA in the mutants and partially restored antibiotic susceptibility 1.5- to 6-fold. This study shows that mutations in acrR are an additional genetic basis for fluoroquinolone resistance.