1,147 research outputs found
Noise Measurement Setup for Quartz Crystal Microbalance
Quartz crystal microbalance (QCM) is a high sensitive chemical sensor which has found widespread spectrum of applications. There are several mechanisms that are related to fluctuation phenomena. Since the aim of our research is oriented to study the sensitivity and influence of different kind of noises on sensor resolution, we modified an existing method to measure the small frequency fluctuation of QCM. The paper describes our measurement setup, in which a quartz crystal oscillator with coated active layers and a reference quartz oscillator are driven by two oscillator circuits. Each one regulates a frequency of a crystal at the minimum impedance which corresponds to the series resonance. A data-acquisition card triggers on the rise-edges of the output signal and stores these corresponding times on which the instantaneous frequency is estimated by own-written software. In comparison to other measurement setups, our approach can acquire immediate change of QCM frequency, thus, chemical processes can be even described on the basis of high-order statistics. The experiments were provided on quartz crystals with the sorption layer of polypyrrole, which is suitable for the construction of QCM humidity sensors
Extracellular volume regulation and growth
We have formalized extracellular and intracellular volume interaction with each other and the influence of these processes on the type of cell growth. The linearized model was verified by stereo metric solution and the results were compared with experimental data. Two theoretical solutions were found: Solution 1, extracellular volume (ECV) was calculated to be about 23% of total body volume (TV). Stereo metric solution suggested the cubic cell cluster formed by 8-cells. This hypothesis (Solution l) explains the ECV to be compatible with the widely accepted value (about 23% of TV). In addition, the 8-cell cluster hypothesis explains the existence of ECV oscillation with the period of about seven days. This hypothesis probably describes the dominant type of growth in humans. Solution 2, in this type of growth, ECV fills about 77% per cent of TV. Instead of the 8-cell cube, in this type of proliferation 4-cells could form a tetrahedron. This type of growth could be beneficial in processes where free space in tissue or organ must be filled for example in peptic ulcer healing and namely in repopulating of free space in a bone after high dose chemotherapy
Is a combination of varenicline and nicotine patch more effective in helping smokers quit than varenicline alone? A randomised controlled trial
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
Comparative analysis of heterogeneity of primary photosynthetic processes within fruticose lichen thalli: Preliminary study of interspecific differences
Two species of fruticose lichens from different habitats and of distinct color, Usnea antarctica and Stereocaulon vesuvianum, were compared using chlorophyll fluorescence imaging in order to study the distribution of primary photosynthetic processes within the thalli. The thallus of U. antarctica is yellow with black tips: in this species chlorophyll containing cells were mostly located in the middle region of the thallus and the highest PS II efficiency was detected in the middle to basal region, as shown by the FV/FM and ΊPSII values. No chlorophyll fluorescence was detected in the apical part of the thallus, indicating that little or no photosynthesis takes place in these tissues. The lichen S. vesuvianum is homogeneously pale grayish green and chlorophyll containing cells are distributed along the thallus with maximum concentration in the middle region. In S. vesuvianum, the highest PS II efficiency was detected in the apical to middle region of the thallus, while the basal portion was found to have the lowest efficiency of primary photochemical reactions. Quenching analysis data confirmed the uneven patterns of primary photosynthetic processes within the thalli of these fruticose lichens
Analytic shock-fronted solutions to a reaction-diffusion equation with negative diffusivity
Reaction-diffusion equations (RDEs) model the spatiotemporal evolution of a
density field according to diffusion and net local changes.
Usually, the diffusivity is positive for all values of , which causes the
density to disperse. However, RDEs with negative diffusivity can model
aggregation, which is the preferred behaviour in some circumstances. In this
paper, we consider a nonlinear RDE with quadratic diffusivity that is negative for . We use a non-classical symmetry to
construct analytic receding time-dependent, colliding wave, and receding
travelling wave solutions. These solutions are initially multi-valued, and we
convert them to single-valued solutions by inserting a shock. We examine
properties of these analytic solutions including their Stefan-like boundary
condition, and perform a phase plane analysis. We also investigate the spectral
stability of the and constant solutions, and prove for certain
and that receding travelling waves are spectrally stable. Additionally,
we introduce an new shock condition where the diffusivity and flux are
continuous across the shock. For diffusivity symmetric about the midpoint of
its zeros, this condition recovers the well-known equal-area rule, but for
non-symmetric diffusivity it results in a different shock position.Comment: 35 pages, 10 figure
Cooling down Levy flights
Let L(t) be a Levy flights process with a stability index \alpha\in(0,2), and
U be an external multi-well potential. A jump-diffusion Z satisfying a
stochastic differential equation dZ(t)=-U'(Z(t-))dt+\sigma(t)dL(t) describes an
evolution of a Levy particle of an `instant temperature' \sigma(t) in an
external force field. The temperature is supposed to decrease polynomially
fast, i.e. \sigma(t)\approx t^{-\theta} for some \theta>0. We discover two
different cooling regimes. If \theta<1/\alpha (slow cooling), the jump
diffusion Z(t) has a non-trivial limiting distribution as t\to \infty, which is
concentrated at the potential's local minima. If \theta>1/\alpha (fast cooling)
the Levy particle gets trapped in one of the potential wells
Phase transition and landscape statistics of the number partitioning problem
The phase transition in the number partitioning problem (NPP), i.e., the
transition from a region in the space of control parameters in which almost all
instances have many solutions to a region in which almost all instances have no
solution, is investigated by examining the energy landscape of this classic
optimization problem. This is achieved by coding the information about the
minimum energy paths connecting pairs of minima into a tree structure, termed a
barrier tree, the leaves and internal nodes of which represent, respectively,
the minima and the lowest energy saddles connecting those minima. Here we apply
several measures of shape (balance and symmetry) as well as of branch lengths
(barrier heights) to the barrier trees that result from the landscape of the
NPP, aiming at identifying traces of the easy/hard transition. We find that it
is not possible to tell the easy regime from the hard one by visual inspection
of the trees or by measuring the barrier heights. Only the {\it difficulty}
measure, given by the maximum value of the ratio between the barrier height and
the energy surplus of local minima, succeeded in detecting traces of the phase
transition in the tree. In adddition, we show that the barrier trees associated
with the NPP are very similar to random trees, contrasting dramatically with
trees associated with the spin-glass and random energy models. We also
examine critically a recent conjecture on the equivalence between the NPP and a
truncated random energy model
- âŠ