655 research outputs found
Aquatic Toxicity of Polyethylene and Microcrystalline Cellulose Microbeads Used as Abrasives in Cosmetics
Microplastics have been part of personal care products for years, but due to microplastic pollution, many companies have replaced microplastics with natural particles, such as microcrystalline cellulose. Although natural particles are considered more environmentally friendly, their ecotoxicological profile is unknown. In this context, the aim of this study was to compare the ecotoxicity of polyethylene and microcrystalline cellulose microbeads, both extracted from a cosmetic product. The effects of the two types of particles on the aquatic macrophyte Lemna minor and the crustacean Daphnia magna, as well as the bioadhesion of the particles to Lemna minor were evaluated. The results showed no significant effects of either particle on the specific growth rate, root length, and chlorophyll content of Lemna minor. The bioadhesion of both types of particles to the plant biomass was comparable. Furthermore, no significant effects were observed on the mobility and body length of Daphnia magna. Thus, the investigated polyethylene and cellulose microbeads showed no significant toxic effects on the tested organisms. However, due to the persistence of polyethylene in the environment, the use of polyethylene microbeads in cosmetics and personal care products should be avoided.
This work is licensed under a Creative Commons Attribution 4.0 International License
Parallel updating cellular automaton models of driven diffusive Frenkel-Kontorova-type systems
Three cellular automaton (CA) models of increasing complexity are introduced
to model driven diffusive systems related to the generalized Frenkel-Kontorova
(FK) models recently proposed by Braun [Phys.Rev.E58, 1311 (1998)]. The models
are defined in terms of parallel updating rules. Simulation results are
presented for these models. The features are qualitatively similar to those
models defined previously in terms of sequentially updating rules. Essential
features of the FK model such as phase transitions, jamming due to atoms in the
immobile state, and hysteresis in the relationship between the fraction of
atoms in the running state and the bias field are captured. Formulating in
terms of parallel updating rules has the advantage that the models can be
treated analytically by following the time evolution of the occupation on every
site of the lattice. Results of this analytical approach are given for the two
simpler models. The steady state properties are found by studying the stable
fixed points of a closed set of dynamical equations obtained within the
approximation of retaining spatial correlations only upto two nearest
neighboring sites. Results are found to be in good agreement with numerical
data.Comment: 26 pages, 4 eps figure
Composite absorbing potentials
The multiple scattering interferences due to the addition of several
contiguous potential units are used to construct composite absorbing potentials
that absorb at an arbitrary set of incident momenta or for a broad momentum
interval.Comment: 9 pages, Revtex, 2 postscript figures. Accepted in Phys. Rev. Let
Tunable linear and quadratic optomechanical coupling for a tilted membrane within an optical cavity: theory and experiment
We present an experimental study of an optomechanical system formed by a
vibrating thin semi-transparent membrane within a high-finesse optical cavity.
We show that the coupling between the optical cavity modes and the vibrational
modes of the membrane can be tuned by varying the membrane position and
orientation. In particular we demonstrate a large quadratic dispersive
optomechanical coupling in correspondence with avoided crossings between
optical cavity modes weakly coupled by scattering at the membrane surface. The
experimental results are well explained by a first order perturbation treatment
of the cavity eigenmodes.Comment: 10 pages, 6 figure
1-Methyl-3-(2-methylphenyl)-3,3a,4,9b-tetrahydro-1H-chromeno[4,3-c][1,2]oxazole-3a-carbonitrile
In the title compound, C19H18N2O2, the five-membered isoxazole ring adopts an envelope conformation and the deviation of the N atom from the mean plane of the isoxazole ring is −0.3256 (11) Å. The pyran ring adopts a half-chair conformation. The isoxazole ring forms dihedral angles of 44.07 (7) and 84.23 (7)° with the pyran and methylbenzene rings, respectively. The molecular structure is stabilized by weak C—H⋯π interactions
Time-Resolved Studies of Stick-Slip Friction in Sheared Granular Layers
Sensitive and fast force measurements are performed on sheared granular
layers undergoing stick-slip motion, along with simultaneous imaging. A full
study has been done for spherical particles with a +-20% size distribution.
Stick-slip motion due to repetitive fluidization of the layer occurs for low
driving velocities. Between major slip events, slight creep occurs that is
variable from one event to the next. The effects of changing the stiffness k
and velocity V of the driving system are studied in detail. The stick-slip
motion is almost periodic for spherical particles over a wide range of
parameters, but becomes irregular when k is large and V is relatively small. At
larger V, the motion becomes smoother and is affected by the inertia of the
upper plate bounding the layer. Measurements of the period T and amplitude A of
the relative motion are presented as a function of V. At a critical value Vc, a
transition to continuous sliding motion occurs that is discontinuous for k not
too large. The time dependence of the instantaneous velocity of the upper plate
and the frictional force produced by the granular layer are determined within
individual slipping events. The force is a multi-valued function of the
instantaneous velocity, with pronounced hysteresis and a sudden drop prior to
resticking. Measurements of vertical displacement reveal a small dilation of
the material (about one tenth of the mean particle size in a layer 20 particles
deep) associated with each slip event. Finally, optical imaging reveals that
localized microscopic rearrangements precede (and follow) each slip event. The
behavior of smooth particles is contrasted with that of rough particles.Comment: 20, pages, 17 figures, to appear in Phys. Rev.
The Generalized Star Product and the Factorization of Scattering Matrices on Graphs
In this article we continue our analysis of Schr\"odinger operators on
arbitrary graphs given as certain Laplace operators. In the present paper we
give the proof of the composition rule for the scattering matrices. This
composition rule gives the scattering matrix of a graph as a generalized star
product of the scattering matrices corresponding to its subgraphs. We perform a
detailed analysis of the generalized star product for arbitrary unitary
matrices. The relation to the theory of transfer matrices is also discussed
Importing genetically altered animals : ensuring quality
The reproducibility of research using laboratory animals requires reliable management of their quality, in particular of their genetics, health and environment, all of which contribute to their phenotypes. The point at which these biological materials are transferred between researchers is particularly sensitive, as it may result in a loss of integrity of the animals and/or their documentation. Here, we describe the various aspects of laboratory animal quality that should be confirmed when sharing rodent research models. We also discuss how repositories of biological materials support the scientific community to ensure the continuity of the quality of laboratory animals. Both the concept of quality and the role of repositories themselves extend to all exchanges of biological materials and all networks that support the sharing of these reagents.Peer reviewe
A single-mode quantum transport in serial-structure geometric scatterers
We study transport in quantum systems consisting of a finite array of N
identical single-channel scatterers. A general expression of the S matrix in
terms of the individual-element data obtained recently for potential scattering
is rederived in this wider context. It shows in particular how the band
spectrum of the infinite periodic system arises in the limit . We
illustrate the result on two kinds of examples. The first are serial graphs
obtained by chaining loops or T-junctions. A detailed discussion is presented
for a finite-periodic "comb"; we show how the resonance poles can be computed
within the Krein formula approach. Another example concerns geometric
scatterers where the individual element consists of a surface with a pair of
leads; we show that apart of the resonances coming from the decoupled-surface
eigenvalues such scatterers exhibit the high-energy behavior typical for the
delta' interaction for the physically interesting couplings.Comment: 36 pages, a LaTeX source file with 2 TeX drawings, 3 ps and 3 jpeg
figures attache
Ki67 index is an independent prognostic factor in epithelioid but not in non-epithelioid malignant pleural mesothelioma: a multicenter study
BACKGROUND: Estimating the prognosis in malignant pleural mesothelioma (MPM) remains challenging. Thus, the prognostic relevance of Ki67 was studied in MPM. METHODS: Ki67 index was determined in a test cohort of 187 cases from three centres. The percentage of Ki67-positive tumour cells was correlated with clinical variables and overall survival (OS). The prognostic power of Ki67 index was compared with other prognostic factors and re-evaluated in an independent cohort (n=98). RESULTS: Patients with Ki67 higher than median (>15%) had significantly (P<0.001) shorter median OS (7.5 months) than those with low Ki67 (19.1 months). After multivariate survival analyses, Ki67 proved to be-beside histology and treatment-an independent prognostic marker in MPM (hazard ratio (HR): 2.1, P<0.001). Interestingly, Ki67 was prognostic exclusively in epithelioid (P<0.001) but not in non-epithelioid subtype. Furthermore, Ki67 index was significantly lower in post-chemotherapy samples when compared with chemo-naive cases. The prognostic power was comparable to other recently published prognostic factors (CRP, fibrinogen, neutrophil-to-leukocyte ratio (NLR) and nuclear grading score) and was recapitulated in the validation cohort (P=0.048). CONCLUSION: This multicentre study demonstrates that Ki67 is an independent and reproducible prognostic factor in epithelioid but not in non-epithelioid MPM and suggests that induction chemotherapy decreases the proliferative capacity of MPM
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