1,995 research outputs found
Latest Developments in Aluminium Reduction
SINCE the end of the Second World War the total global production of virgin aluminium has increased very rapidly. In the year 1945 it amounted to approximately 0.85 million tons a year, whereas for 1960 about 5 million tons may be
estimated. The production of aluminium has grown during this time to be one of the most important industries. Although the aluminium works have often been subject to a certain criticism on account of the inflexibility of the extraction process-since in the main the fused salt ele-ctrolysis has not altered until this day-developments in the matter of cell design and operating methods have made considerable progress. With regard to further awaited expansion of aluminium production plants, there exists a lively interest to expedite developments to improve cell and building layout and to ensure a more economic operat-ion in order to reduce the previous relatively high inve-stment and operating costs.
Experience tells us that two types of electrolytic cells have proved their merits, namely :
(a) Cells with prebaked anodes
(b) Cells with self-baking anode
Description of non-specific DNA-protein interaction and facilitated diffusion with a dynamical model
We propose a dynamical model for non-specific DNA-protein interaction, which
is based on the 'bead-spring' model previously developed by other groups, and
investigate its properties using Brownian Dynamics simulations. We show that
the model successfully reproduces some of the observed properties of real
systems and predictions of kinetic models. For example, sampling of the DNA
sequence by the protein proceeds via a succession of 3d motion in the solvent,
1d sliding along the sequence, short hops between neighboring sites, and
intersegmental transfers. Moreover, facilitated diffusion takes place in a
certain range of values of the protein effective charge, that is, the
combination of 1d sliding and 3d motion leads to faster DNA sampling than pure
3d motion. At last, the number of base pairs visited during a sliding event is
comparable to the values deduced from single-molecule experiments. We also
point out and discuss some discrepancies between the predictions of this model
and some recent experimental results as well as some hypotheses and predictions
of kinetic models
Combined population dynamics and entropy modelling supports patient stratification in chronic myeloid leukemia
Modelling the parameters of multistep carcinogenesis is key for a better understanding of cancer
progression, biomarker identification and the design of individualized therapies. Using chronic
myeloid leukemia (CML) as a paradigm for hierarchical disease evolution we show that combined
population dynamic modelling and CML patient biopsy genomic analysis enables patient stratification
at unprecedented resolution. Linking CD34+ similarity as a disease progression marker to patientderived
gene expression entropy separated established CML progression stages and uncovered
additional heterogeneity within disease stages. Importantly, our patient data informed model enables
quantitative approximation of individual patients’ disease history within chronic phase (CP) and
significantly separates “early” from “late” CP. Our findings provide a novel rationale for personalized
and genome-informed disease progression risk assessment that is independent and complementary to
conventional measures of CML disease burden and prognosis
Handling and analysis of ices in cryostats and glove boxes in view of cometary samples
Comet nucleus sample return mission and other return missions from planets and satellites need equipment for handling and analysis of icy samples at low temperatures under vacuum or protective gas. Two methods are reported which were developed for analysis of small icy samples and which are modified for larger samples in cometary matter simulation experiments (KOSI). A conventional optical cryostat system was modified to allow for transport of samples at 5 K, ion beam irradiation, and measurement in an off-line optical spectrophotometer. The new system consists of a removable window plug containing nozzles for condensation of water and volatiles onto a cold finger. This plug can be removed in a vacuum system, changed against another plug (e.g., with other windows (IR, VIS, VUV) or other nozzles). While open, the samples can be treated under vacuum with cooling by manipulators (cut, removal, sample taking, irradiation with light, photons, or ions). After bringing the plug back, the samples can be moved to another site of analysis. For handling the 30 cm diameter mineral-ice samples from the KOSI experiments an 80x80x80 cm glove box made out of plexiglass was used. The samples were kept in a liquid nitrogen bath, which was filled from the outside. A stream a dry N2 and evaporating gas from the bath purified the glove box from impurity gases and, in particular, H2O, which otherwise would condense onto the samples
Optimizing information flow in small genetic networks. I
In order to survive, reproduce and (in multicellular organisms)
differentiate, cells must control the concentrations of the myriad different
proteins that are encoded in the genome. The precision of this control is
limited by the inevitable randomness of individual molecular events. Here we
explore how cells can maximize their control power in the presence of these
physical limits; formally, we solve the theoretical problem of maximizing the
information transferred from inputs to outputs when the number of available
molecules is held fixed. We start with the simplest version of the problem, in
which a single transcription factor protein controls the readout of one or more
genes by binding to DNA. We further simplify by assuming that this regulatory
network operates in steady state, that the noise is small relative to the
available dynamic range, and that the target genes do not interact. Even in
this simple limit, we find a surprisingly rich set of optimal solutions.
Importantly, for each locally optimal regulatory network, all parameters are
determined once the physical constraints on the number of available molecules
are specified. Although we are solving an over--simplified version of the
problem facing real cells, we see parallels between the structure of these
optimal solutions and the behavior of actual genetic regulatory networks.
Subsequent papers will discuss more complete versions of the problem
Toward Lower Organic Environments in Astromaterial Sample Curation for Diverse Collections
Great interest was taken during the frenzied pace of the Apollo lunar sample return to achieve and monitor organic cleanliness. Yet, the first mission resulted in higher organic contamination to samples than desired. But improvements were accomplished by Apollo 12 [1]. Quarantine complicated the goal of achieving organic cleanliness by requiring negative pressure glovebox containment environments, proximity of animal, plant and microbial organic sources, and use of organic sterilants in protocols. A special low organic laboratory was set up at University of California Berkeley (UCB) to cleanly subdivide a subset of samples [2, 3, 4]. Nevertheless, the basic approach of handling rocks and regolith inside of a positive pressure stainless steel glovebox and restrict-ing the tool and container materials allowed in the gloveboxes was established by the last Apollo sample re-turn. In the last 40 years, the collections have grown to encompass Antarctic meteorites, Cosmic Dust, Genesis solar wind, Stardust comet grains and Hayabusa asteroid grains. Each of these collections have unique curation requirements for organic contamination monitor-ing and control. Here is described some changes allowed by improved technology or driven by changes in environmental regulations and economy, concluding with comments on organic witness wafers. Future sample return missions (OSIRIS-Rex; Mars; comets) will require extremely low levels of organic contamination in spacecraft collection and thus similarly low levels in curation. JSC Curation is undertaking a program to document organic baseline levels in current operations and devise ways to reduce those levels
Evaluation of Epithelial Integrity with Various Transepithelial Corneal Cross-Linking Protocols for Treatment of Keratoconus
Purpose. Corneal collagen cross-linking (CXL) has been demonstrated to stiffen cornea and halt progression of ectasia. The original protocol requires debridement of central corneal epithelium to facilitate diffusion of a riboflavin solution to stroma. Recently, transepithelial CXL has been proposed to reduce risk of complications associated with epithelial removal. Aim of the study is to evaluate the impact of various transepithelial riboflavin delivery protocols on corneal epithelium in regard to pain and epithelial integrity in the early postoperative period. Methods. One hundred and sixty six eyes of 104 subjects affected by progressive keratoconus underwent transepithelial CXL using 6 different riboflavin application protocols. Postoperatively, epithelial integrity was evaluated at slit lamp and patients were queried regarding their ocular pain level. Results. One eye had a corneal infection associated with an epithelial defect. No other adverse event including endothelial decompensation or endothelial damage was observed, except for epithelial damages. Incidence of epithelial defects varied from 0 to 63%. Incidence of reported pain varied from 0 to 83%. Conclusion. Different transepithelial cross-linking protocols have varying impacts on epithelial integrity. At present, it seems impossible to have sufficient riboflavin penetration without any epithelial disruption. A compromise between efficacy and epithelial integrity has to be found
Correlated optical and structural analyses of individual GaAsP/GaP core–shell nanowires
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