Squat, stoop, or something in between?

This article reviews the empirical and theoretical bases for recommendations regarding lifting technique. Lifting from postures involving extreme lumbar vertebral flexion, (approximately 60degrees of lumbar flexion, characterised by absence of electromyographical activity in erector spinae) has the potential to contribute to damage to ligaments and intervertebral discs, especially if combined with lateral flexion or rotation. The only appropriate recommendation regarding posture of the lumbar spine during lifting is to avoid postures involving extreme lumbar vertebral flexion (and rotation and lateral flexion). There is no empirical basis for avoiding postures involving moderate lumbar vertebral flexion, and no justification for advocating lifting from a full squat posture. Further, lifting from semi-squat postures, involving a moderate range of flexion at both knees and trunk, allows a pattern of interjoint coordination which appears to be functional in reducing muscular effort. Lifting training is generally ineffective, and there is unlikely to be a single best technique which is appropriate in all situations. Consequently, it may be preferable to provide education in general lifting guidelines and assist lifters to discover individually appropriate postures and patterns of movement. The article concludes by presenting recommendations for lifting technique which are justified by current knowledge.

Comparisons between bone and cementum compositions and the possible basis for their layered appearances

In humans, age estimation from the adult skeleton represents an attempt to determine chronological age based on growth and maturational events. In teeth, such events can be characterized by appositional growth layers in midroot cementum. The purpose of this study was to determine the underlying cause of the layered microstructure of human midroot cementum. Whether cementum growth layers are caused by changes in relative mineralization, collagen packing and/or orientation, or by variations in organic matrix apposition was investigated by subjecting midroot sections of human canine teeth to analysis using polarized light and scanning electron microscopy (SEM). Polarized light was used to examine transverse midroot sections in both mineralized and demineralized states. Mineralized sections were also reexamined following subsequent decollagenization. Polarized light was additionally used in the examination of mineralized sections taken transversely, longitudinally, and obliquely from the same tooth root. From the birefringence patterns it was concluded that collagen orientation does not change with varying section plane. Instead, the mineral phase was most responsible for the birefringence of the cementum. SEM studies suggested that neither collagen packing nor collagen orientation change across the width of the cementum, confirming and validating the results of the polarized light examination. Also, SEM analysis using electron backscatter and the electron probe suggested no changes in the mean atomic number density, calcium, phosphate, and sulfur levels across the width of the cementum. Therefore, we conclude that crystalline orientation and/or size is responsible for the layered appearance of cementum. (Bone 30:386-392; 2002) (C) 2002 by Elsevier Science Inc. All rights reserved.

Role of oxygen in the nitrous oxide/carbon reaction

An investigation of the role of oxygen in the nitrous oxide/carbon reaction was carried out on various carbon samples (both graphitic and nongraphitic) over a range of temperatures and partial pressures. Previous work reported that oxygen strongly inhibited the nitrous oxide/carbon reaction. Large ratios of O-2/N2O were used in all previous work. In this work, the O-2/N2O ratio was kept below 1, and we found that oxygen did not inhibit the rate of the C + N2O reaction. Instead, the rate of the reaction in the presence of oxygen was essentially that predicted by the two independent reactions, nitrous oxide/carbon and oxygen/carbon, occurring simultaneously. A simple theoretical explanation is given for the observations, both past and present, on the basis of competitive chemisorption of nitrous oxide and oxygen on active sites.

Characterization of the retinoid orphan-related receptor-alpha coactivator binding interface: A structural basis for ligand-independent transcription

The retinoid orphan-related receptor-alpha (RORalpha) is a member of the ROR subfamily of orphan receptors and acts as a constitutive activator of transcription in the absence of exogenous ligands. To understand the basis of this activity, we constructed a homology model of Rill using the closely related TRbeta as a template. Molecular modeling suggested that bulky hydrophobic side chains occupy the RORa ligand cavity leaving a small but distinct cavity that may be involved in receptor stabilization. This model was subject to docking simulation with a receptor-interacting peptide from the steroid receptor coactivator, GR-interacting protein-1, which delineated a coactivator binding surface consisting of the signature motif spanning helices 3-5 and helix 12 [activation function 2 (AF2)]. Probing this surface with scanning alanine mutagenesis showed structural and functional equivalence between homologous residues of RORalpha and TRbeta. This was surprising (given that Rill is a ligand-independent activator, whereas TRbeta has an absolute requirement for ligand) and prompted us to use molecular modeling to identify differences between Rill and TRbeta in the way that the All helix interacts with the rest of the receptor. Modeling highlighted a nonconserved amino acid in helix 11 of RORa (Phe491) and a short-length of 3.10 helix at the N terminus of AF2 which we suggest i) ensures that AF2 is locked permanently in the holoconformation described for other liganded receptors and thus 2) enables ligand-independent recruitment of coactivators. Consistent with this, mutation of RORa Phe491 to either methionine or alanine (methionine is the homologous residue in TRbeta), reduced and ablated transcriptional activation and recruitment of coactivators, respectively. Furthermore, we were able to reconstitute transcriptional activity for both a deletion mutant of Ill lacking All and Phe491 Met, by overexpression of a GAL-AF2 fusion protein, demonstrating ligand-independent recruitment of AF2 and a role for Phe491 in recruiting AF2.

The intuitive basis of implicature: relevance theoretic implicitness versus gricean implying

The notion of implicature was first introduced by Paul Grice (1967, 1989), who defined it essentially as what is communicated less what is said. This definition contributed in part to the proliferation of a large number of different species of implicature by neo-Griceans. Relevance theorists have responded to this by proposing a shift back to the distinction between "explicit" & "implicit" meaning (corresponding to "explicature" & "implicature," respectively). However, they appear to have pared down the concept of implicature too much, ignoring phenomena that may be better treated as implicatures in their overgeneralization of the concept of explicature. These problems have their roots in the fact that explicit & implicit meaning intuitively overlap & thus do not provide a suitable basis for distinguishing implicature from other types of pragmatic phenomena. An alternative conceptualization of implicature based on the concept of "implying" with which Grice originally associated his notion of implicature is thus proposed. From this definition, it emerges that implicature constitutes something else inferred by the addressee that is not literally said by the speaker. Instead, it is meant in addition to what the speaker literally says & is consequently defeasible like all other types of pragmatic phenomena. 1 Figure, 60 References. Adapted from the source document

Simulation of the micro-physics of rocks using LSMearth

The particle-based Lattice Solid Model (LSM) was developed to provide a basis to study the physics of rocks and the nonlinear dynamics of earthquakes (MORA and PLACE, 1994; PLACE and MORA, 1999). A new modular and flexible LSM approach has been developed that allows different microphysics to be easily included in or removed from the model. The approach provides a virtual laboratory where numerical experiments can easily be set up and all measurable quantities visualised. The proposed approach provides a means to simulate complex phenomena such as fracturing or localisation processes, and enables the effect of different micro-physics on macroscopic behaviour to be studied. The initial 2-D model is extended to allow three-dimensional simulations to be performed and particles of different sizes to be specified. Numerical bi-axial compression experiments under different confining pressure are used to calibrate the model. By tuning the different microscopic parameters (such as coefficient of friction, microscopic strength and distribution of grain sizes), the macroscopic strength of the material and can be adjusted to be in agreement with laboratory experiments, and the orientation of fractures is consistent with the theoretical value predicted based on Mohr-Coulomb diagram. Simulations indicate that 3-D numerical models have different macroscopic properties than in 2-D and, hence, the model must be recalibrated for 3-D simulations. These numerical experiments illustrate that the new approach is capable of simulating typical rock fracture behaviour. The new model provides a basis to investigate nucleation, rupture and slip pulse propagation in complex fault zones without the previous model limitations of a regular low-level surface geometry and being restricted to two-dimensions.

gl(2 vertical bar 2) current superalgebra and non-unitary conformal field theory

Motivated by application of current superalgebras in the study of disordered systems such as the random XY and Dirac models, we investigate gl(2\2) current superalgebra at general level k. We construct its free field representation and corresponding Sugawara energy-momentum tensor in the non-standard basis. Three screen currents of the first kind are also presented. (C) 2003 Elsevier B.V. All rights reserved.

A structural basis for the selection of dominant alpha beta T cell receptors in antiviral immunity

We have examined the basis for immunodominant or public TCR usage in an antiviral CTL response. Residues encoded by each of the highly selected genetic elements of an immunodominant clonotype recognizing Epstein-Barr virus were critical to the antigen specificity of the receptor. Upon recognizing antigen the immunodominant TCR undergoes extensive conformational changes in the complementarity determining regions (CDRs), including the disruption of the canonical structures of the germline-encoded CDR1alpha and CDR2alpha loops to produce an enhanced fit with the HLA-peptide complex. TCR ligation induces conformational changes in the TCRalpha constant domain thought to form part of the docking site for CD3epsilon. These findings indicate that TCR immunodominance is associated with structural properties conferring receptor specificity and suggest a novel structural link between TCR ligation and intracellular signaling.

Numerical study of hydrogenic effective mass theory for an impurity P donor in Si in the presence of an electric field and interfaces

In this paper we examine the effects of varying several experimental parameters in the Kane quantum computer architecture: A-gate voltage, the qubit depth below the silicon oxide barrier, and the back gate depth to explore how these variables affect the electron density of the donor electron. In particular, we calculate the resonance frequency of the donor nuclei as a function of these parameters. To do this we calculated the donor electron wave function variationally using an effective-mass Hamiltonian approach, using a basis of deformed hydrogenic orbitals. This approach was then extended to include the electric-field Hamiltonian and the silicon host geometry. We found that the phosphorous donor electron wave function was very sensitive to all the experimental variables studied in our work, and thus to optimize the operation of these devices it is necessary to control all parameters varied in this paper.

Molecular basis of sulfonylurea herbicide inhibition of acetohydroxyacid synthase

Acetohydroxyacid synthase (AHAS) (acetolactate synthase, EC 4.1.3.18) catalyzes the first step in branchedchain amino acid biosynthesis and is the target for sulfonylurea and imidazolinone herbicides. These compounds are potent and selective inhibitors, but their binding site on AHAS has not been elucidated. Here we report the 2.8 Angstrom resolution crystal structure of yeast AHAS in complex with a sulfonylurea herbicide, chlorimuron ethyl. The inhibitor, which has a K-i of 3.3 nM blocks access to the active site and contacts multiple residues where mutation results in herbicide resistance. The structure provides a starting point for the rational design of further herbicidal compounds.