1,668 research outputs found
Superconducting proximity effect in interacting double-dot systems
We study subgap transport from a superconductor through a double quantum dot
with large on-site Coulomb repulsion to two normal leads. Non-local
superconducting correlations in the double dot are induced by the proximity to
the superconducting lead, detectable in non-local Andreev transport that splits
Cooper pairs in locally separated, spin-entangled electrons. We find that the
-- characteristics are strongly asymmetric: for a large bias voltage of
certain polarity, transport is blocked by populating the double dot with states
whose spin symmetry is incompatible with the superconductor. Furthermore, by
tuning gate voltages one has access to splitting of the Andreev excitation
energies, which is visible in the differential conductance.Comment: 5 pages, 4 figure
Catching VY Sculptoris in a low state
Context. In the context of a large campaign to determine the system
parameters of high mass transfer cataclysmic variables, we found VY Scl in a
low state in 2008. Aims. Making use of this low state, we study the stellar
components of the binary with little influence of the normally dominating
accretion disc. Methods. Time-resolved spectroscopy and photometry of VY Scl
taken during the low state are presented. We analysed the light-curve and
radial velocity curve and use time-resolved spectroscopy to calculate Doppler
maps of the dominant emission lines. Results. The spectra show narrow emission
lines of Halpha, Hbeta, HeI, NaID, and FeII, as well as faint TiO absorption
bands that trace the motion of the irradiated secondary star, and Halpha and
HeI emission line wings that trace the motion of the white dwarf. From these
radial velocities, we find an orbital period of 3.84 h, and put constraints on
binary parameters such as the mass ratio M2/M1 of 0.43 and the inclination of
15 deg. With a secondary's mass between 0.3 and 0.35 Msol, we derive the mass
for the white dwarf as M1 = 0.6-0.1 Msol.Comment: 8 pages, 9 figures, accepted for publication in A&
Factors influencing MOW deinking : laboratory scale studies
The deinking of MOW is examined at laboratorial scale. The effect of deinking aids, pre-washing and mixing are studied. The operating conditions during pulp treatment affect the pulp and paper properties, interfering with the mechanism of ink removal and modifying the ink particle characteristics. Pre-washing the pulp facilitates the deinking process. Cellulolytic enzymes and deinking chemicals are comparable in terms of ink removal ability.Portucel Vian
Evidence for reduced magnetic braking in polars from binary population models
We present the first population synthesis of synchronous magnetic cataclysmic variables, called polars, taking into account the effect of the white dwarf (WD) magnetic field on angular momentum loss. We implemented the reduced magnetic braking (MB) model proposed by Li, Wu & Wickramasinghe into the Binary Stellar Evolution (BSE) code recently calibrated for cataclysmic variable (CV) evolution. We then compared separately our predictions for polars and non-magnetic CVs with a large and homogeneous sample of observed CVs from the Sloan Digital Sky Survey. We found that the predicted orbital period distributions and space densities agree with the observations if period bouncers are excluded. For polars, we also find agreement between predicted and observed mass transfer rates, while the mass transfer rates of non-magnetic CVs with periods ≳3 h drastically disagree with those derived from observations. Our results provide strong evidence that the reduced MB model for the evolution of highly magnetized accreting WDs can explain the observed properties of polars. The remaining main issues in our understanding of CV evolution are the origin of the large number of highly magnetic WDs, the large scatter of the observed mass transfer rates for non-magnetic systems with periods ≳3 h, and the absence of period bouncers in observed samples
Enzymatic versus chemical deinking of non-impact ink printed paper
Enzymatic versus chemical deinking is examined for MOW and photocopy prints. Several enzymatic preparations and two
fibre/ink particle separation methods are tested. Deinking was monitored by image analysis and standard pulp and paper characterisation
procedures. The effectiveness of the fibre/ink particle separation method depends on the ink particle’s size: for smaller
particles a washing step is recommended whereas for larger particles, the use of flotation is necessary. The enzymatic treatment
is a competitive alternative for MOW and photocopy paper deinking. However, the process requires the selection of an adequate
enzymatic preparation for each paper grade
Refining and enzymatic treatment of secondary fibres for paperboard production : Cyberflex measurements of fibre flexibility
Recycling is generally affected by secondary fibre quality. High temperature and pressure during the drying stage causes irreversible changes in fibre morphology, which is the mainly responsible for the considerable reduction in the swelling and bonding ability (strength and number of bonds) [1, 2, 3]. Additionally, the reduced dewatering ability of these pulps is a major problem during paper manufacture as they decrease the speed on the paper machine and worsen sheet formation [4]. Secondary fibre upgrade is difficult and sometimes unpredictable, as the samples to be treated vary along with their history. Traditional upgrade methodologies have been used to improve secondary fibre properties, but the results are most of the times insufficient [1, 5]. Different reports suggest that treating pulps with enzymes and refining could overcome these problems [4, 6, 7, 8, 9]. More recently, Cellulose-Binding Domains (CBD’s) usage has been shown as an interesting tool to modify recycled fibres properties
Modification of secondary pulp fibre fractions by enzymatic treatment
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Laboratory paper pulp deinking : an evaluation based on image analysis, ISO Brightness and ERIC
Image analysis, ERIC and ISO Brightness
measurements were used to evaluate the
effectiveness of laboratory deinking
assays. The accurate measurement of the
residual ink amount is difficult and the
results depend on the methodology used.
The three techniques correlate only when
the same paper pulp sample is analysed
and when the ink particle size distribution
profile is similar. As the relative amount of
each particle size depends on the deinking
protocol used, the ink removal effectiveness
is measured differently according
to each test method. Image analysis was
shown to be the most reliable method
Enzymatic depolymerisation of cellulose
Cellulose degree of polymerisation (DP) was determined in paper pulps and commercial powder celluloses before and after the enzymatic treatment with a blend of cellulases and hemicellulases. Three different methods were used: (i) chemical method, based on the measurement of the cellulose reducing power; (ii) viscosimetry; and (iii) gel permeation chromatography. Although based in very different principles, the three methods find similar DP values in the case of pure cellulose with narrow molecular weight distributions.
The chemical method is more sensitive to detect enzymatic depolymerisation and appears to provide a good estimation of the number-average DP.
GPC data offers more detailed information about the enzymes mode of action on the fibres, showing that cellulose hydrolysis in the presence of the commercial preparation Celluclast 1.5L follows a layer-by-layer solubilisation mechanism.University of Beira Interior – Department of Paper Science and Technology; Portucel Viana
Enzymatic modification of paper fibres
The enzymatic mode of action in paper fibre upgrading is still uncertain. In an attempt to clarify how enzymes modify pulp and paper properties, several parameters were analysed in the present work: (i) thermal analysis of the water–solid surface interactions; (ii) fibre cake permeability; (iii) particle size analysis. The results obtained suggest that enzymes modify the interfacial properties of fibres, increasing the water affinity, which in turn change the technical properties of pulp and paper,
such as drainability and strength. The modification of paper and pulps following a treatment with cellulosebinding domains further supports this hypothesis
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