Rheological properties vs. local dynamics in model disordered materials at low temperature.

We study the rheological response at low temperature of a sheared model disordered material as a function of the bond rigidity. We find that the flow curves follow a Herschel-Bulkley law, whatever is the bond rigidity, with an exponent close to 0.5. Interestingly, the apparent viscosity can be related to a single relevant time scale t rel, suggesting a strong connection between the local dynamics and the global mechanical behaviour. We propose a model based on the competition between the nucleation and the avalanche-like propagation of spatial strain heterogeneities. This model can explain the Herschel-Bulkley exponent on the basis of the size dependence of the heterogeneities on the shear rate.

Partial characterization of the gene encoding myoadenylate deaminase from the teleost fish Platichthys flesus.

AMP-deaminase (AMPD, EC 3.5.4.6), which catalyzes the irreversible hydrolytic deamination of AMP to IMP and ammonia, is an important energy-related enzyme. The partial genomic sequence of the gene encoding myoadenylate deaminase (AMPD1) from the teleost fish Platichthys flesus was determined. The amino acid sequence of P. flesus AMPD1 shows 82% homology with that of the teleost fish Danio rerio. Comparison of genomic sequences of P. flesus and Rattus norvegicus reveals a high degree of conservation of both sequence and structural organization. A phylogenetic analysis of AMPD sequences shows that bony fish and mammalian AMPD1s arise by duplication of a common primordial gene.

Continuum constitutive laws to describe acoustic attenuation in glasses.

Nowadays metamaterials are at the focus of an intense research as promising for thermal and acoustic engineering. However, the computational cost associated to the large system size required for correctly simulating them imposes the use of finite-elements simulations, developing continuum models, able to grasp the physics at play without entering in the atomistic details. Still, a correct description should be able to reproduce not only the extrinsic scattering sources on waves propagation, as introduced by the metamaterial microstructure, but also the intrinsic wave attenuation of the material itself. This becomes dramatically important when the metamaterial is made out of a glass, which is intrinsically highly dissipative and with a wave attenuation strongly dependent on frequency. Here we propose a continuum mechanical model for a viscoelastic medium, able to bridge atomic and macroscopic scale in amorphous materials and describe phonon attenuation due to atomistic mechanisms, characterized by a defined frequency dependence. This represents a first decisive step for investigating the effect of a complex nano- or microstructure on acoustic attenuation, while including the atomistic contribution as well.

Development of isohomoeoallelic lines within the wheat cv. Courtot for high molecular weight glutenin subunits: transfer of the Glu-D1 locus to chromosome 1A.

Wheat quality depends on protein composition and grain protein content. High molecular weight glutenin subunits (HMW-GS) play an important role in determining the viscoelastic properties of gluten. In an attempt to improve the bread-making quality of hexaploid wheat by elaborating novel HMW-GS combinations, a fragment of wheat chromosome 1D containing the Glu-D1 locus encoding the Dx2+Dy12 subunits was translocated to the long arm of chromosome 1A using the ph1b mutation. The partially isohomoeoallelic line selected was characterized using cytogenetical and molecular approaches to assess the amount of chromatin introgressed in the translocated 1A chromosome. Triple-target genomic in situ hybridization indicated that the translocated 1A chromosome had a terminal 1D segment representing 25% of the length of the recombinant long arm. The translocation was also identified on the long arm using molecular markers, and its length was estimated with a minimum of 91 cM. Proteome analysis was performed on total endosperm proteins. Out of the 152 major spots detected, 9 spots were up-regulated and 4 spots were down-regulated. Most of these proteins were identified as alpha-, beta-, gamma-gliadins assigned to the chromosomes of homoeologous groups 1 and 6. Quantitative variations in the HMW-GS were only observed in subunit Dy12 in response to duplication of the Glu-D1 locus.

Existence of a rotational axial component in the human humeral medullary canal.

To explain surgical findings, we studied the anatomy of the human humeral medullary canal on a series of 28 bones in 16 patients and 9 dried bones. A methodology is described to find angle of medullary canal on CT scans regarding to an epicondylar reference axis. We found a constant tri-dimensional spiral shape of the medullary canal in the distal part of the bone. The relations between this first description and the literature are discussed.

Enhancement and anticipation of the Ioffe-Regel crossover in amorphous/nanocrystalline composites.

Nanocomposites made of crystalline nanoinclusions embedded in an amorphous matrix are at the forefront of current research for energy harvesting applications. However, the microscopic mechanisms leading alternatively to an effectively reduced or enhanced thermal transport still escape understanding. In this work, we present a molecular dynamics simulation study of model systems, where for the first time we combine a microscopic investigation of phonon dynamics with the macroscopic thermal conductivity calculation, to shed light on thermal transport in these materials. We clearly show that crystalline nanoinclusions represent a novel scattering source for vibrational waves, modifying the nature of low energy vibrations and significantly anticipating the propagative-to-diffusive crossover (Ioffe-Regel), usually located at energies of few THz in amorphous materials. Moreover, this crossover position can be tuned by changing the elastic contrast between nanoinclusions and the matrix, and anticipated by a factor as large as 10 for a harder inclusion. While the propagative contribution to thermal transport is drastically reduced, the calculated thermal conductivity is not significantly affected in the chosen system, as the diffusive contribution dominates heat transport when all phonons are thermally populated. These findings allow finally to understand the panoply of contradictory results reported on thermal transport in nanocomposites and give clear indications to the characteristics that the parent phases should have for efficiently reducing heat transport in a nanocomposite.

Propagative and diffusive regimes of acoustic damping in bulk amorphous material.

In amorphous solids, a non-negligible part of thermal conductivity results from phonon scattering on the structural disorder. The conversion of acoustic energy into thermal energy is often measured by the dynamical dtructure factor (DSF) thanks to inelastic neutron or x-ray scattering. The DSF is used to quantify the dispersion relation of phonons, together with their damping. However, the connection of the dynamical structure factor with dynamical attenuation of wave packets in glasses is still a matter of debate. We focus here on the analysis of wave-packet propagation in numerical models of amorphous silicon. We show that the damped harmonic oscillator model fits of the dynamical structure factors give a good estimate of the wave packets mean free path, only below the Ioffe-Regel frequency. Above the Ioffe-Regel frequency and below the mobility edge, a pure diffusive regime without a definite mean free path is observed. The high-frequency mobility edge is characteristic of a transition to localized vibrations. Below the Ioffe-Regel frequency, a mixed regime is evidenced at intermediate frequencies, with a coexistence of propagative and diffusive wave fronts. The transition between these different regimes is analyzed in detail and reveals a complex dynamics for energy transport, thus raising the question of the correct modeling of thermal transport in amorphous materials.

New Simplified Screening Method for Postprandial Hypotension in Older People.

BACKGROUND: Postprandial hypotension (PPH) is an important disorder in the older people that remain underdiagnosed. The reference PPH diagnostic method is too demanding, because blood pressure (BP) needs to be measured 8 times in 2 hours. OBJECTIVES: Our primary objective was to define a new simplified PPH diagnostic method and to evaluate its performances. DESIGN: We conducted a cross-sectional study. SETTING: Two geriatric rehabilitation units in France. PARTICIPANTS: 104 patients (70 women, 34 men) with high risk of PPH were included. MEASUREMENTS: BP was measured twice before the midday meal in seated position at the table, and every 15 minutes for 90 minutes after the end of the meal. Receiver Operating Characteristic curves were plotted for each postprandial BP measure to determine the best postprandial measure in terms of sensitivity and specificity. The optimal diagnostic threshold was calculated with Youden's index according to BP difference before and after the meal. RESULTS: A new simplified diagnostic method is proposed: a decrease of at least 10 mmHg systolic BP between BP measures before the meal and 75 minutes after the end of the meal. This new method had a sensitivity of 82% (95%CI 66 - 92) and a specificity of 91% (95%CI 81 - 97). CONCLUSION: This new diagnostic method is fast, efficient and suitable for everyday use. It could improve PPH diagnosis in older people. Larger studies are needed to validate it.

Evidence for a slightly deleterious effect of intron polymorphisms at the EF1alpha gene in the deep-sea hydrothermal vent bivalve Bathymodiolus.

A multilocus analysis was initiated in order to infer the general effect of demography and the indirect effect of positive selection on some chromosome segments in Bathymodiolus. Mussels of the genus Bathymodiolus inhabit the very hostile, fragmented and variable environment of deep-sea hydrothermal vents which is thought to cause recurrent population bottlenecks via extinction/colonisation processes and adaptation to new environmental conditions. In the course of this work we discovered that the assumption of neutrality of non-coding polymorphisms usually made in genome scan experiments was likely to be violated at one of the loci we analysed. The direct effect of slight purifying selection on non-coding polymorphisms shares many resemblances with the indirect effect of positive selection through genetic hitchhiking. Combining polymorphism with divergence data for several closely related species allowed us to obtain different expectations for the direct effect of negative selection and the indirect effect of positive selection. We observed a strong excess of rare non-coding polymorphisms at the second intron of the EF1alpha gene in the two species Bathymodiolus azoricus and Bathymodiolus thermophilus, while two other loci, the mitochondrial COI gene and an intron of the Lysozyme gene, did not exhibit such a deviation. In addition, the divergence rate of the EF1alpha intron was estimated to be unexpectedly low when calibrated using the closure of the Panama Isthmus that interrupted gene flow between the two species. The polymorphism to divergence ratio was similar to the one observed for the other two loci, in accordance to the hypothesis of purifying selection. We conclude that slight purifying selection is likely to act on polymorphic intronic mutations of the EF1alpha second intron and discuss the possible relationship with the specific biology of Bathymodiolus mussels.

Peroxiredoxin 6 gene: a new physiological and genetic indicator of multiple environmental stress response in Pacific oyster Crassostrea gigas.

Peroxiredoxin 6 is a 1-cysteine peroxiredoxin involved in antioxidant processes. We characterised the full-length cDNA and genomic sequence of the gene encoding peroxiredoxin 6 (CgPrx6) in the Pacific oyster, Crassostrea gigas. A phylogenetic analysis of Prx6 sequences showed that the CgPrx6 segregates between vertebrate and invertebrate groups. We analysed the expression of mRNA coding for CgPrx6 using RT-PCR in gills and digestive gland of oysters sampled in different contaminated and reference estuaries of the Atlantic French coast. We also studied CgPrx6 exon 6 polymorphism by PCR-SSCP in the same populations. Our results showed that CgPrx6 gene expression was highly regulated in the estuaries showing differential contamination levels, as expression increased with pollution level. Polymorphism analysis revealed no significant allelic frequency variations between populations. However, heterozygote deficiency seems to occur in the most contaminated estuaries, suggesting a potential selective effect of environmental stress on heterozygote frequency. Finally, the use of CgPrx6 as a possible marker to monitor stress exposure in disturbed ecosystems is discussed.

Molecular identification and expression of differentially regulated genes of the European flounder, Platichthys flesus, submitted to pesticide exposure.

Effects of pesticide exposure on the European flounder, Platichthys flesus, were investigated using a suppression subtractive hybridization method (SSH) to identify up- and down-regulated genes after a 30-day exposure to herbicides (a cocktail of atrazine, diuron, and isoproturon, and a single herbicide, glyphosate). A total of 256 expressed gene sequences were identified as having the potential for being differentially expressed, of which 116 could be identified by homology with databased sequences. The metabolic functions with which they are associated include energy production, general metabolism, signaling, transport, immune system, and structure. Expression of 14 of these genes was analyzed in liver, muscle, and gills by reverse transcriptase-polymerase chain reaction (RT-PCR) under experimental conditions (0, 15, and 30 days of exposure) and under field conditions (sampling in two estuaries displaying different levels of pesticide contamination). This study provides a first basis for studying the response of fish to pesticide exposure and allows the characterization of new potential genetic markers of pesticide contamination in the field.

Mapping between atomistic simulations and Eshelby inclusions in the shear deformation of an amorphous silicon model.

In this paper we perform quasistatic shear simulations of model amorphous silicon bulk samples with Stillinger-Weber-type potentials. Local plastic rearrangements identified based on local energy variations are fitted through their displacement fields on collections of Eshelby spherical inclusions, allowing determination of their transformation strain tensors. The latter are then used to quantitatively reproduce atomistic stress-strain curves, in terms of both shear and pressure components. We demonstrate that our methodology is able to capture the plastic behavior predicted by different Stillinger-Weber potentials, in particular, their different shear tension coupling. These calculations justify the decomposition of plasticity into shear transformations used so far in mesoscale models and provide atomic-scale parameters that can be used to limit the empiricism needed in such models up to now.

Impact of pressure on plastic yield in amorphous solids with open structure.

Plasticity in amorphous silica is unusual: The yield stress decreases with hydrostatic pressure, in contrast to the Mohr-Coulomb response commonly found in more compact materials such as bulk metallic glasses. To better understand this response, we have carried out molecular dynamics simulations of plastic response in a model glass with open structure. The simulations reproduce the anomalous dependence of yield stress with pressure and also correctly predict that the plastic response turns to normal once the material has been fully compacted. We also show that the overall shape of the yield surface is consistent with a quadratic behavior predicted assuming local buckling of the structure, a point of view that fits well into the present understanding of the deformation mechanisms of amorphous silica. The results also confirm that free volume is an adequate internal variable for a continuum scale description of the plastic response of amorphous silica. Finally, we also investigate the long-range correlations between rearrangement events. We find that strong intermittency is observed when the structure remains open, while compaction results in more homogeneous rearrangements. These findings are in agreement with recent results on the effect of compression on the middle range order in silicate glasses and also suggest that the well-known volume recovery of densified silica at relatively low temperatures is in fact a form of aging.

Boson peak and Ioffe-Regel criterion in amorphous siliconlike materials: The effect of bond directionality.

The vibrational properties of model amorphous materials are studied by combining complete analysis of the vibration modes, dynamical structure factor, and energy diffusivity with exact diagonalization of the dynamical matrix and the kernel polynomial method, which allows a study of very large system sizes. Different materials are studied that differ only by the bending rigidity of the interactions in a Stillinger-Weber modelization used to describe amorphous silicon. The local bending rigidity can thus be used as a control parameter, to tune the sound velocity together with local bonds directionality. It is shown that for all the systems studied, the upper limit of the Boson peak corresponds to the Ioffe-Regel criterion for transverse waves, as well as to a minimum of the diffusivity. The Boson peak is followed by a diffusivity's increase supported by longitudinal phonons. The Ioffe-Regel criterion for transverse waves corresponds to a common characteristic mean-free path of 5-7 Å (which is slightly bigger for longitudinal phonons), while the fine structure of the vibrational density of states is shown to be sensitive to the local bending rigidity.

Quantitative decrease of human cytochrome c oxidase during development: evidences for a post-transcriptional regulation.

In an earlier study, we showed that cytochrome c oxidase activity, measured in mitochondria isolated from human muscular biopsies, decreased steadily and substantially between the age of four years and adulthood (P < 0.05), whereas complexes I and III activity remained constant. The present study investigates a number of possible causes for this change in activity: although there is a drop in the apparent Vmax, neither the apparent enzyme Km, nor the cellular mtDNA concentration shows any variations over the studied period. Steady-state concentrations of mitochondrial gene transcripts (CO I. CO II, CO III, but also 12S, cytochrome b, or ND4) increase within this age group, indicating an overall increase in mitochondrial genome expression. Concentrations of transcripts of nuclear genes CO IV, CO Vb, and CO VIaH likewise show an increase, albeit less marked. On the other hand, heme aa3 levels and concentrations of mitochondrial (CO II) or nuclear (CO IV, CO VIIaH) subunits, estimated using specific antibodies, correlate closely with enzymatic activity and show a parallel decrease between 4 and 20 years. The observed decrease in complex IV activity is thus quantitative, and subject to post-transcriptional and/or post-translational regulation.

Enzymatic activities of mitochondrial respiratory complexes from children muscular biopsies. Age-related evolutions.

Measurements were performed to determine maximum enzymatic activities of citrate synthetase and respiratory complexes I, III, and IV of mitochondria obtained from muscular biopsies in control children. The significant number of determinations carried out (43 different biopsies in controls aged 3.8 to 19.1 years) permits the formulation of a table of statistically validated reference values for these activities. These values are independent of sex of the controls, and of the studied muscles. Citrate synthetase activity, which remains stable in this age range, thus constitutes a good internal indicator of mitochondrial activity. Complexes I and III manifest activity which does not vary with age. On the other hand, cytochrome oxidase activity shows a highly significant decrease in this age group. This decrease may be correlated with qualitative changes (subunits VIa and VIIa) in composition of this complex.

Clinical staging versus laparotomy and combined modality with MOPP versus ABVD in early-stage Hodgkin's disease: the H6 twin randomized trials from the European Organization for Research and Treatment of Cancer Lymphoma Cooperative Group.

PURPOSE: To compare (1) clinical staging and irradiation alone versus staging laparotomy and treatment adaptation in patients with a favorable prognosis (H6F); (2) two combined modalities in patients with an unfavorable prognosis (H6U). PATIENTS AND METHODS: The H6F trial (n = 262) consisted of randomization to clinical staging plus subtotal nodal irradiation (STNI) or to staging laparotomy plus treatment adaptation (adjuvant chemotherapy [CT] only in the 33% with negative laparotomy). The H6U trial (n = 316) consisted of no laparotomy, randomization to mechlorethamine, vincristine, procarbazine, and prednisone (MOPP) or doxorubicin, bleomycin, vinblastine, and dacarbazine (ABVD), and mantle irradiation. RESULTS: In the H6F trial, 6-year freedom from progression (FFP) rates (78% v 83%; P = .27) were similar in clinical and laparotomy stagings, respectively. Survival rates were 93% and 89%, due to laparotomy-related deaths. In the H6U trial, the ABVD arm had superior results (6-year FFP rate, 88% v 76%; P = .01), but they were not significant for survival (91% v 85%; P = .22). CT discontinuation due to hematologic intolerance occurred more often with MOPP (14.5% v 7.3%). Decrease of the pulmonary vital capacity ([VC] < 70% of the theoretic value) was observed more frequently after ABVD than after MOPP (12% v 2%; P = .08), with two lethal pulmonary insufficiencies occurring in the ABVD arm. No modification of the isotopic left ventricular ejection fraction (LVEF) occurred. Gonadal toxicity was less in the ABVD arm. CONCLUSION: Early-stage patients benefit from treatment adaptation to initial characteristics in terms of tumor control and late toxicities. Staging laparotomy before STNI may be deleted even in favorable patients at no cost to survival or FFP. In unfavorable patients, ABVD achieved better results than MOPP, at lower hematologic and gonadal cost. Therefore, despite its pulmonary toxicity, ABVD is the best choice to design improved CT regimens associated with mantle irradiation.

Clinical stages I and II Hodgkin's disease: a specifically tailored therapy according to prognostic factors.

The H5 program in clinical stage (CS) I to II supradiaphragmatic Hodgkin's disease (HD) was tailored to prognostic factors identified in former European Organization for the Research and Treatment of Cancer (EORTC) studies. Among the 494 adult patients included in the study, the 237 patients belonging to the favorable group (H5F) underwent a staging laparotomy (Sx) in order to select the patients who could be treated with limited radiotherapy (RT) only. Thus, 198 patients (84%) with negative laparotomy were treated with RT alone and randomized to either mantle irradiation (M) or extended field mantle plus para-aortic (M + PA) irradiation. Complete remission (CR) was achieved in 99% of the patients. There was no difference in the 6-year relapse-free survival (RFS) rate (74% and 72%, respectively) or survival rate (96% and 89%). Therefore, Sx helped to define those patients who could be treated with M alone in contrast to those who required more aggressive therapy. The 39 patients with positive laparotomy were treated as the unfavorable group (H5U) from onset and randomized to either total/subtotal nodal irradiation (TNI/STNI) or a sandwiched mechlorethamine, vincristine, procarbazine, and prednisone (MOPP) X 3, M irradiation, MOPP X 3 protocol (3M). Although the RFS rate was higher in the 3M arm (100% v 53%; P = .002), the 6-year survival was not significantly different between the two arms (overall, 92%). In the 257 patients with initial unfavorable disease, the Sx was avoided. They were randomized to either TNI/STNI or 3M. In complete responders (96%), the 6-year RFS was 91% in the 3M arm and 77% in the TNI/STNI arm (P = .02). The pattern of failure differed in the two arms: the inverted Y and spleen irradiation controlled occult infradiaphragmatic disease better than MOPP; conversely, less patients begun on MOPP recurred in the involved mantle areas. The difference in 6-year actuarial total survival (TS) (89% and 82%; P = .05 in favor of the 3M arm) was not retrieved after exclusion of the unrelated deaths from the analysis. The two arms produced similar TS in patients under 40 years of age. TNI retains interest, especially in young men wishing to preserve fertility. The overall result shows that when treatment is tailored to initial prognostic factors, excellent results can be obtained in all patient subgroups at minimal morbidity and toxic cost.