Repression and reactivation of the variant surface glycoprotein gene in Trypanosoma brucei

AbstractRapid repression of variant surface glycoprotein (VSG) synthesis is an early event during the in vitro transformation of Trypanosoma brucei from coated bloodstream forms to uncoated procyclic cells. Repression occurs at the transcriptional level and is triggered by the combined action of two signals: a reduction in temperature from 37 to 27°C and the addition of the citric acid cycle intermediates citrate and cis-aconitate. It is shown that synthesis of VSG mRNA can be reactivated up to 8 h after triggering differentiation by releasing either one or both of the signals. After 30 h repression is irreversible. The results suggest that transformation of bloodstream forms to procyclic cells proceeds through a reversible phase to an irreversible committed state. A reversible repression of VSG mRNA synthesis is also observed upon inhibition of protein synthesis in bloodstream forms at 37°C

Seshadri) -Corning Glass Works

-ceramic ball/ceramic disc (kit 4): Slight abrasion of the ball and slight smoothing of the disc surface. In The results of the first round of the VAMAS Round Robin Comparison show that a good reproducibility of the numeric friction and wear data has been obtained which can be summarized in terms of the relative standard deviations (s r and s R according to ASTM Standard E 691 divided by the mean value) as follows: -Reproducibility of the friction data: within laboratories: ± 9 to ±13 percent interlaboratory: ±18 to ±20 percent -Reproducibility of specimen wear data within laboratories: ± 5 to ± 7 percent interlaboratory: ±15 to ±20 percent -Reproducibility of system wear data within laboratories: ±14 percent interlaboratory: ±29 to ±38 percent These results show that the overall reproducibility of systematic friction and wear measurements is comparable with that of other complex engineering quantities provided that the tests are performed under well controlled conditions

Roughness and wettability of surfaces in boundary lubricated scuffing wear

The diversity of multidisciplinary approaches suggests that fundamentals of scuffing require systemic, complex multi-scale and multi-physics analysis of an irreversible process as it is postulated in present study. That is probably one of the reasons of lack of unequivocal model of this irreversible transitional process from stable more or less lubricated wear to scuffing described only by one or few authors in equation(s) form. Therefore, it is useful to characterize the tribological surface properties in frame of systemic approach looking simultaneously for the optimal compromise between rheological, morphological and physicochemical features of contacting surface's layer. Hypothetical role connected to any group of features in the topological approach is elucidated and experimentally confirmed via the wettability, strongly combined with surface roughness and surface free energy. Due to the fact that the free energy is directly related to the surface wettability it can as well affect the scuffing activation process. For scientific and rhetoric reasons some selected results of limited boundary lubrication investigations under double blind trial conditions in case of gear oil with anti-wear (AW) and extreme pressure (EP) additives are elucidated here. The results issued from scuffing tests on AISI 4140 ground steel burnished under different forces in order to generate different surface roughness, residual stresses and surface energy are analysed. It was stated and numerically correlated that the wettability by lubricating medium influences the scuffing resistance. Additionally, the dependence of wettability on selected parameters of roughness and a time to scuffing activation have been stated. On that basis, it is proposed to reinforce concept of "oleophilic" and "oleophobic" properties of metallic surfaces as autonomous invariants determining the activation of catastrophic wear process under boundary lubricated conditions

Rolling friction of a viscous sphere on a hard plane

A first-principle continuum-mechanics expression for the rolling friction coefficient is obtained for the rolling motion of a viscoelastic sphere on a hard plane. It relates the friction coefficient to the viscous and elastic constants of the sphere material. The relation obtained refers to the case when the deformation of the sphere $\xi$ is small, the velocity of the sphere $V$ is much less than the speed of sound in the material and when the characteristic time $\xi/V$ is much larger than the dissipative relaxation times of the viscoelastic material. To our knowledge this is the first ``first-principle'' expression of the rolling friction coefficient which does not contain empirical parameters.Comment: 6 pages, 2 figure

Cytochrome oxidase subunit VI of Trypanosoma brucei is imported without a cleaved presequence and is developmentally regulated at both RNA and protein levels

Mitochondrial respiration in the African trypanosome undergoes dramatic developmental stage regulation. This requires co-ordinated control of components encoded by both the nuclear genome and the kinetoplast, the unusual mitochondrial genome of these parasites. As a model for understanding the co-ordination of these genomes, we have examined the regulation and mitochondrial import of a nuclear-encoded component of the cytochrome oxidase complex, cytochrome oxidase subunit VI (COXVI). By generating transgenic trypanosomes expressing intact or mutant forms of this protein, we demonstrate that COXVI is not imported using a conventional cleaved presequence and show that sequences at the N-terminus of the protein are necessary for correct mitochondrial sorting. Analyses of endogenous and transgenic COXVI mRNA and protein expression in parasites undergoing developmental stage differentiation demonstrates a temporal order of control involving regulation in the abundance of, first, mRNA and then protein. This represents the first dissection of the regulation and import of a nuclear-encoded protein into the cytochrome oxidase complex in these organisms, which were among the earliest eukaryotes to possess a mitochondrion

Radiological diagnostics in neonates with different types of congenital cystic adenomatoid malformation of the lungs (CCAM) treated in Polish Mother's Memorial Hospital Research Institute (PMMHRI) in 1991-2005

Background: Congenital cystic adenomatoid malformation of the lungs (CCAM) is a rare congenital malformation of the respiratory tract. Authors present possibilities of the diagnostics of neonates with presumed CCAM based on radiological and morphological assessment of the respiratory tract. Clinical course of the CCAM may vary from uneventful to serious with different stage of the respiratory distress. The aim of the study was to establish diagnostic and clinical criteria of CCAM for neonates based on postnatal diagnostics in the reference centre. Material/Methods: We studied 27 cases of neonates with different types of CCAM (type I, II, III) who had been diagnosed and/or treated in the Neonatal Department of PMMHRI in 01.01.1991-31.03.2005. The diagnosis was established based on clinical course of the malformation, chest x-ray and CT of the neonate's lungs, autopsy and/or histopathology. Results: In the Neonatal Department of PMMHRI in 01.01.1991-31.03.2005 we observed 8 cases of CCAM type I (29,7%), 10 cases of CCAM type II (37%) and 9 cases of CCAM type III (33,3%). Diagnostic criteria were established based on radiological diagnostics of 17 cases and were confirmed by pathology. In 10 remaining cases of CCAM diagnosis was established by authopsy. Differential diagnosis included diaphragmatic hernia, bronchogenic cyst, enterogenic cyst, lung sequestrqtion, congenital lobar emphysema, hypoplasia or agenesis of the lungs, pneumonia/RDS. The guideline was established. Conclusions: 1. In case of CCAM suspicion monitoring in reference center is required 2. Surgical treatment should be applied based on the postnatal radiological diagnosis. 3. In case of CCAM in neonate complete differential diagnosis is required. 4. Asymptomatic course of CCAM or with a very few signs from respiratory tract can be difficult for identification both clinical and radiological

A sensor for direct measurement of small convective heat fluxes: Validation and application to micro-structured surfaces

A sensor for measuring small convective heat flows (<0.2 W/cm^2) from micro-structured surfaces is designed and tested. This sensor {exploits the notion of thermal guard and is purposely designed} to deal with metal samples made by additive manufacturing, {such as} direct metal laser sintering (DMLS). For validation purposes, we utilize both experimental literature data and a computational fluid dynamic (CFD) model: Maximum and average deviations from CDF model in terms of the Nusselt number are on the order of +/- 13.7 % and +/- 6.3 %, respectively while deviations from literature data are even smaller. Similar works in the literature often have the necessity of maintaining one-directional heat flows along the main dimension of a conducting bar using insulating materials. Such an approach can be critical for small fluxes due to the curse of heat conduction losses along secondary directions. As a result, it is necessary to estimate those secondary fluxes (e.g. by numerical models), thus making the measurement difficult and indirect. On the other hand, depending on the manufacturing accuracy, the present sensor enables to practically reduce at will those losses, with direct measurement of the heat flux. To our knowledge, the adoption of thermal guard is not a common practice in convective heat transfer, especially when local measurements are of interest. We hope that this study may (i) shed light on the usefulness of the approach in this field; and (ii) provide an effective tool for future investigation on electronic cooling and convective heat transfer enhancement by micro-/nano-structured surfaces. Owing to a number of features of the proposed device, we suggest that it can be prospectively utilized in the near future (i) for industrial applications (due to simplicity and robustness of the design); (ii) for high temperature measurements (unlike foil sensors, no delamination issues can be experienced); (iii) in the context of micro-electromechanical systems (MEMS) (easy to miniaturize)