On the creep ringing behavior of semi-dilute polyacrylamide and polyethylene oxide solutions

Aqueous polyacrylamide solutions (PAAm) and polyethylene oxide solutions (PE) of 5, 10, and 15 wt% were characterized under creep measurements. To the best of our knowledge it is the first time that the creep ringing method is used to study these types of polymeric materials. The rheometric measurements were carried out using an Anton Paar MCR 502 rheometer, equipped with a parallel plate measuring geometry with sandblasted surfaces. By performing a stepwise adjustment of the gap, it was possible to keep the maximum normal force during the loading procedure below 5 N. In addition, after each step the time evolution of the relaxation was recorded. In this way, the measurements could be carried out on fully relaxed samples. Systematic creep measurements showed that the initial response correlates to the moment of inertia of the instrument and the geometry. All samples exhibited dumping oscillations. For both PAAm and PE, a profound effect of the polymer concentration on the characteristic ringing frequency and amplitude of oscillations was found. Although, the results are qualitatively comparable, PE exhibits much higher storage and loss moduli. Independent of the magnitude of the applied stress, the initial ringing data coincide until the end of the ringing behavior. However, the long-term creep behavior is significantly affected by the magnitude of the applied stress. In addition, we studied the impact of NaCl and the molecular weight of the polymer on the viscoelasticity of the PAAm solutions. We found that the ionic strength affects both the frequency and duration of ringing. In addition, we found that decreasing the molecular weight of PAAm decreases the amplitude of oscillation and ringing frequency. If the instrument inertia is taken into account, the Jeffreys model provides a satisfying fit to the creep data. All values of the viscoelastic parameters presented here were obtained by fitting this model to the creep compliance curve. The present study shows that the creep ringing method is an extremely helpful since the short- and long-term creep compliance can be simultaneously obtained. Please click Additional Files below to see the full abstract

Steady-state activation and modulation of the synaptic-type α1β2γ2L GABAA receptor by combinations of physiological and clinical ligands

The synaptic α1β2γ2 GAB

Large-scale molecular dynamics simulations of shock induced plasticity in tantalum single crystals

We report on large-scale non-equilibrium molecular dynamics (NEMD) simulations of shock wave compression in Ta single crystals. The atomic interactions are modeled via a recently developed and optimized embedded-atom method (EAM) potential for Ta, which reproduces the equation of state up to 200 GPa. We examined the elastic-plastic transition and shock wave structure for wave propagation along the low index directions: (100), (110) and (111). Shock waves along (100) and (111) exhibit an elastic precursor followed by a plastic wave for particle velocities below 1.1 km/s for (100) and 1.4 km/s for (111). The nature of the plastic deformation along (110) is dominated by twinning for pressures above 41 GPa

Bio-inspired Tensegrity Soft Modular Robots

In this paper, we introduce a design principle to develop novel soft modular robots based on tensegrity structures and inspired by the cytoskeleton of living cells. We describe a novel strategy to realize tensegrity structures using planar manufacturing techniques, such as 3D printing. We use this strategy to develop icosahedron tensegrity structures with programmable variable stiffness that can deform in a three-dimensional space. We also describe a tendon-driven contraction mechanism to actively control the deformation of the tensegrity mod-ules. Finally, we validate the approach in a modular locomotory worm as a proof of concept.Comment: 12 pages, 7 figures, submitted to Living Machine conference 201

Activation of the rat α1β2ε GABAA receptor by orthosteric and allosteric agonists

GAB

A reduced model for shock and detonation waves. II. The reactive case

We present a mesoscopic model for reactive shock waves, which extends a previous model proposed in [G. Stoltz, Europhys. Lett. 76 (2006), 849]. A complex molecule (or a group of molecules) is replaced by a single mesoparticle, evolving according to some Dissipative Particle Dynamics. Chemical reactions can be handled in a mean way by considering an additional variable per particle describing a rate of reaction. The evolution of this rate is governed by the kinetics of a reversible exothermic reaction. Numerical results give profiles in qualitative agreement with all-atom studies

The Production of Hospitable Space: Commercial Propositions and Consumer Co-Creation in a Bar Operation

This paper examines the processes through which a commercial bar is transformed into a hospitable space. Drawing on a study of a venue patronized by lesbian, gay, bisexual and transsexual/transgender consumers, it considers how social and commercial forms of hospitality are mobilized. The paper argues that hospitable space has an ideological, normative and situational dimension. More specifically, it suggests the bar’s operation is tied to a set of ideological conceptions, which become the potential basis of association and disassociation among consumers. It examines the forces and processes that shape who participates in the production and consumption of hospitality and how. Finally, it considers the situational, emergent nature of hospitality and the discontinuous production of hospitable space. Rather than focusing exclusively on host-guest or provider-customer relations, which dominates existing work on hospitality, the paper examines how consumers’ perceptions, actions and interactions shape the production of hospitality. By doing so the paper offers an alternative approach to understanding queer spaces, bar operation as well as hospitality

Vertical-external-cavity surface-emitting lasers and quantum dot lasers

The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and also quantum information devices. In particular, in the field of semiconductor lasers, QDs were introduced as a superior alternative to quantum wells to suppress the temperature dependence of the threshold current in vertical-external-cavity surface-emitting lasers (VECSELs). In this work, a review of properties and development of semiconductor VECSEL devices and QD laser devices is given. Based on the features of VECSEL devices, the main emphasis is put on the recent development of technological approach on semiconductor QD VECSELs. Then, from the viewpoint of both single QD nanolaser and cavity quantum electrodynamics (QED), a single-QD-cavity system resulting from the strong coupling of QD cavity is presented. A difference of this review from the other existing works on semiconductor VECSEL devices is that we will cover both the fundamental aspects and technological approaches of QD VECSEL devices. And lastly, the presented review here has provided a deep insight into useful guideline for the development of QD VECSEL technology and future quantum functional nanophotonic devices and monolithic photonic integrated circuits (MPhICs).Comment: 21 pages, 4 figures. arXiv admin note: text overlap with arXiv:0904.369