50 research outputs found
A mechanistic perspective on plastically flexible coordination polymers
Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon. We present here the first example of a plastically flexible oneâdimensional (1D) coordination polymer. The compound [Zn(ÎŒâCl)2(3,5âdichloropyridine)2]n is flexible over two crystallographic faces. Remarkably, the single crystal remains intact when bent to 180°. A combination of microscopy, diffraction, and spectroscopic studies have been used to probe the structural response of the crystal lattice to mechanical bending. Deformation of the covalent polymer chains does not appear to be responsible for the observed macroscopic bending. Instead, our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers. Moreover, our calculations propose a cause of the different mechanical properties of this compound and a structurally similar elastic material
Soliton ratchets induced by ac forces with harmonic mixing
The ratchet dynamics of a kink (topological soliton) of a dissipative
sine-Gordon equation in the presence of ac forces with harmonic mixing (at
least bi-harmonic) of zero mean is studied. The dependence of the kink mean
velocity on system parameters is investigated numerically and the results are
compared with a perturbation analysis based on a point particle representation
of the soliton. We find that first order perturbative calculations lead to
incomplete descriptions, due to the important role played by the soliton-phonon
interaction in establishing the phenomenon. The role played by the temporal
symmetry of the system in establishing soliton ratchets is also emphasized. In
particular, we show the existence of an asymmetric internal mode on the kink
profile which couples to the kink translational mode through the damping in the
system. Effective soliton transport is achieved when the internal mode and the
external force get phase locked. We find that for kinks driven by bi-harmonic
drivers consisting of the superposition of a fundamental driver with its first
odd harmonic, the transport arises only due to this {\it internal mode}
mechanism, while for bi-harmonic drivers with even harmonic superposition, also
a point-particle contribution to the drift velocity is present. The phenomenon
is robust enough to survive the presence of thermal noise in the system and can
lead to several interesting physical applications.Comment: 9 pages, 13 figure
Stochastic Resonance in Ion Channels Characterized by Information Theory
We identify a unifying measure for stochastic resonance (SR) in voltage
dependent ion channels which comprises periodic (conventional), aperiodic and
nonstationary SR. Within a simplest setting, the gating dynamics is governed by
two-state conductance fluctuations, which switch at random time points between
two values. The corresponding continuous time point process is analyzed by
virtue of information theory. In pursuing this goal we evaluate for our
dynamics the tau-information, the mutual information and the rate of
information gain. As a main result we find an analytical formula for the rate
of information gain that solely involves the probability of the two channel
states and their noise averaged rates. For small voltage signals it simplifies
to a handy expression. Our findings are applied to study SR in a potassium
channel. We find that SR occurs only when the closed state is predominantly
dwelled. Upon increasing the probability for the open channel state the
application of an extra dose of noise monotonically deteriorates the rate of
information gain, i.e., no SR behavior occurs.Comment: 10 pages, 2 figures, to appear in Phys. Rev.
Whole-genome sequencing reveals host factors underlying critical COVID-19
Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genesâincluding reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)âin critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease
Coppered-tungsten seals through hard glass
A process is described for providing tungsten with an adherent and structurally sound sheath of copper, which flows into and fills up any cracks. This process can be used for making vacuum-tight seals through glass with split tungsten
Rectification phenomena exhibited by natural and sulphurized galena
Specimens of n-type galena were sulphurized, either by a wet chemical process or by exposure to sulphur vapour at various temperatures, and the resulting changes in rectification characteristics were observed, both with dc instruments and at 3 000 Mc/s, using various cats-whiskers. According to treatment given, either an improved n-type rectification was obtained or the polarity was changed to p-type The results are briefly discussed in the light of present-day rectification theory
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A Mechanistic Perspective on Plastically Flexible Coordination Polymers
Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon. We present here the first example of a plastically flexible one-dimensional (1D) coordination polymer. The compound [Zn(Ό-Cl)2(3,5-dichloropyridine)2]n is flexible over two crystallographic faces. Remarkably, the single crystal remains intact when bent to 180°. A combination of microscopy, diffraction, and spectroscopic studies have been used to probe the structural response of the crystal lattice to mechanical bending. Deformation of the covalent polymer chains does not appear to be responsible for the observed macroscopic bending. Instead, our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers. Moreover, our calculations propose a cause of the different mechanical properties of this compound and a structurally similar elastic material. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA