Stability of dancing Volvox

Biflagellate algal cells of the genus Volvox form spherical colonies that propel themselves, vertically upwards in still fluid, by the coordinated beating of thousands of flagella, that also cause the colonies to rotate about their vertical axes. When they are swimming in a chamber of finite depth, pairs (or more) of Volvox carteri colonies were observed by Drescher et al. [Phys. Rev. Lett. 102, 168101 (2009)] to exhibit hydrodynamic bound states when they are close to a rigid horizontal boundary. When the boundary is above, the colonies are attracted to each other and orbit around each other in a `waltz'; when the boundary is below they perform more complex `minuet' motions. These dances are simulated in the present paper, using a novel `spherical squirmer' model of a colony in which, instead of a time-independent but $\theta$-dependent tangential velocity being imposed on the spherical surface (radius $a$; $\theta$ is the polar angle), a time-independent and uniform tangential shear stress is applied to the fluid on a sphere of radius $(1+\epsilon)a, \epsilon \ll 1$, where $\epsilon a$ represents the length of the flagella. The fluid must satisfy the no-slip condition on the sphere at radius $a$. In addition to the shear stress, the motions depend on two dimensionless parameters that describe the effect of gravity on a colony: $F_g$, proportional to the ratio of the sedimentation speed of a non-swimming colony to its swimming speed, and $G_{bh}$, that represents the fact that colonies are bottom-heavy..

Single leg drop jump is affected by physical capacities in male soccer players following ACL reconstruction

Single leg drop jump (SLDJ) assessment is commonly used during the later stages of rehabilitation to identify residual deficits in reactive strength but the effects of physical capacity on kinetic and kinematic variables in male soccer players following ACL reconstruction remains unknown. Isokinetic knee extension strength, kinematics from an inertial measurement unit 3D system and SLDJ performance variables and mechanics derived from a force plate were measured in 64 professional soccer players (24.7 ± 3.4 years) prior to return to sport (RTS). SLDJ between-limb differences were measured (part 1) and players were divided into tertiles based on isokinetic knee extension strength (weak, moderate and strong) and reactive strength index (RSI) (low, medium and high) (part 2). Moderate to large significant differences between the ACL reconstructed and uninjured limb in SLDJ performance (d = 0.92 – 1.05), kinetic (d = 0.62 – 0.71) and kinematic variables (d = 0.56) were evident. Stronger athletes jumped higher (p = 0.002; d = 0.85), produced greater concentric (p = 0.001; d = 0.85) and eccentric power (p = 0.002; d = 0.84). Similar findings were present for RSI, but the effects were larger (d = 1.52 – 3.84). Weaker players, and in particular those who had lower RSI, displayed landing mechanics indicative of a “stiff” knee movement strategy. SLDJ performance, kinetic and kinematic differences were identified between-limbs in soccer players at the end of their rehabilitation following ACL reconstruction. Players with lower knee extension strength and RSI displayed reduced performance and kinetic strategies associated with increased injury risk

Combining transcriptome analyses and virus induced gene silencing to identify genes in the Rpp4-mediated asian soybean rust resistance Pathway.

Six Asian Soybean Rust (ASR) resistance loci have been identified and mapped in soybean genome: Rpp1 (Resistance to Phakopsora pachyrhizi 1), Rpp2, Rpp3, Rpp4, Rpp5 and Rpp6. Of particular interest is Rpp4, which has remained stable and confers resistance against Phakopsora pachyrhizi isolates from around the world. Sequencing of the region harboring Rpp4 in the susceptible cultivar Williams 82 (Wm82) and the resistant cultivar (PI459025B) genotype identified a cluster of CC-NBS-LRR resistance genes. Meyers et al. (2009) developed Virus Induced Gene Silencing constructs from the LRR regions of the Wm82 Rpp4 candidate genes to confirm that orthologous genes were responsible for resistance in the resistant parent (PI459025B). In this study, RNA samples extracted from the same Rpp4 LRR silenced and empty vector treated plants, also infected with P. pachyrhizi (described by Meyer et al., 2009) were compared using the GeneChip® Soybean Genome Array (Affymetrix®). Since the plant samples differed only in the expression of Rpp4, comparisons of these samples would identify genes downstream of Rpp4 in the signaling pathway. In total, 383 differentially expressed probes were identified, many with functions related to defense. While the time point analyzed was late in defense signaling, bioinformatic approaches were useful in characterizing the defense response and identify transcription factors regulating the response

Interplay between geometry and flow distribution in an airway tree

Uniform fluid flow distribution in a symmetric volume can be realized through a symmetric branched tree. It is shown here, however, that the flow partitioning can be highly sensitive to deviations from exact symmetry if inertial effects are present. This is found by direct numerical simulation of the Navier-Stokes equations in a 3D tree geometry. The flow asymmetry is quantified and found to depend on the Reynolds number. Moreover, for a given Reynolds number, we show that the flow distribution depends on the aspect ratio of the branching elements as well as their angular arrangement. Our results indicate that physiological variability should be severely restricted in order to ensure uniform fluid distribution in a tree. This study suggests that any non-uniformity in the air flow distribution in human lungs should be influenced by the respiratory conditions, rest or hard exercise

Measurement of the critical DNA lesions produced by antibody-directed enzyme prodrug therapy (ADEPT) in vitro, in vivo and in clinical material

An antibody-directed enzyme prodrug therapy (ADEPT) system against CEA-positive tumours is currently in phase I clinical trials. It consists of a prodrug, 4-[N,N-bis(2-iodoethyl) amino] phenoxycarbonyl L -glutamic acid (ZD2767P) and a conjugate of the F(ab')2 anti-CEA antibody A5B7 and the bacterial enzyme carboxypeptidase G2 (CPG2). ZD2767P is converted by antibody-targeted CPG2 into an active bifunctional alkylating drug (ZD2767) at the tumour site. The IC 50 value of the prodrug against the human colorectal tumour LS174T cell line was 55 ± 9 μM following a 1 h exposure. In contrast, co-incubation of ZD2767P with CPG2 resulted in 229-fold increase in activity. Using a modified comet assay, DNA interstrand cross links (ISC) were detected within 1 h of ZD2767P + CPG2 treatment and were repaired by 24 h. A clear dose–response was seen between the level of ISC, growth inhibition and ZD2767 concentration. Administration of a therapeutic dose of ZD2767P 72 h after the F(ab′)2 A5B7 conjugate to mice bearing LS147T xenografts resulted in extensive ISC in the tumour after 1 h; repair was seen at 24 h. Tumour biopsies and peripheral lymphocytes were studied in 5 patients on the ADEPT phase I clinical trial. In 4 patients no ISC were detected. These patients also demonstrated poor localization of conjugate and no tumour response was seen. However a significant level of ISC was detected in one tumour biopsy, which also showed evidence of conjugate localization and clinical response. These studies demonstrate the application of the comet assay in the measurement of ISC in vitro and in clinical material and confirm that activation of ZD2767P results in the formation of DNA crosslinks. © 2001 Cancer Research Campaign http://www.bjcancer.co