Effects of a nonlinear bath at low temperatures

We use the numerical flow-equation renormalization method to study a nonlinear bath at low temperatures. The model of our nonlinear bath consists of a single two-level system coupled to a linear oscillator bath. The effects of this nonlinear bath are analyzed by coupling it to a spin, whose relaxational dynamics under the action of the bath is studied by calculating spin-spin correlation functions. As a first result, we derive flow equations for a general four-level system coupled to an oscillator bath, valid at low temperatures. We then treat the two-level system coupled to our nonlinear bath as a special case of the dissipative four-level system. We compare the effects of the nonlinear bath with those obtained using an effective linear bath, and study the differences between the two cases at low temperatures.Comment: 15 pages, 7 figure

Pivotal Role of Reduced Glutathione in Oxygen-induced Regulation of the Na + /K + Pump in Mouse Erythrocyte Membranes

This study addresses the mechanisms of oxygen-induced regulation of ion transport pathways in mouse erythrocyte, specifically focusing on the role of cellular redox state and ATP levels. Mouse erythrocytes possess Na+/K+ pump, K+-Cl− and Na+-K+-2Cl− cotransporters that have been shown to be potential targets of oxygen. The activity of neither cotransporter changed in response to hypoxia-reoxygenation. In contrast, the Na+/K+ pump responded to hypoxic treatment with reversible inhibition. Hypoxia-induced inhibition was abolished in Na+-loaded cells, revealing no effect of O2 on the maximal operation rate of the pump. Notably, the inhibitory effect of hypoxia was not followed by changes in cellular ATP levels. Hypoxic exposure did, however, lead to a rapid increase in cellular glutathione (GSH) levels. Decreasing GSH to normoxic levels under hypoxic conditions abolished hypoxia-induced inhibition of the pump. Furthermore, GSH added to the incubation medium was able to mimic hypoxia-induced inhibition. Taken together these data suggest a pivotal role of intracellular GSH in oxygen-induced modulation of the Na+/K+ pump activit

Quantum Dissipative Dynamics of the Magnetic Resonance Force Microscope in the Single-Spin Detection Limit

We study a model of a magnetic resonance force microscope (MRFM) based on the cyclic adiabatic inversion technique as a high-resolution tool to detect single electron spins. We investigate the quantum dynamics of spin and cantilever in the presence of coupling to an environment. To obtain the reduced dynamics of the combined system of spin and cantilever, we use the Feynman-Vernon influence functional and get results valid at any temperature as well as at arbitrary system-bath coupling strength. We propose that the MRFM can be used as a quantum measurement device, i.e., not only to detect the modulus of the spin but also its direction

Non-Markoffian effects of a simple nonlinear bath

We analyze a model of a nonlinear bath consisting of a single two-level system coupled to a linear bath (a classical noise force in the limit considered here). This allows us to study the effects of a nonlinear, non-Markoffian bath in a particularly simple situation. We analyze the effects of this bath onto the dynamics of a spin by calculating the decay of the equilibrium correlator of the spin's z-component. The exact results are compared with those obtained using three commonly used approximations: a Markoffian master equation for the spin dynamics, a weak-coupling approximation, and the substitution of a linear bath for the original nonlinear bath.Comment: 7 pages, 6 figure

In vitro blood flow and cell-free layer in hyperbolic microchannels: visualizations and measurments

Red blood cells (RBCs) in microchannels has tendency to undergo axial migration due to the parabolic velocity profile, which results in a high shear stress around wall that forces the RBC to move towards the centre induced by the tank treading motion of the RBC membrane. As a result there is a formation of a cell free layer (CFL) with extremely low concentration of cells. Based on this phenomenon, several works have proposed microfluidic designs to separate the suspending physiological fluid from whole in vitro blood. This study aims to characterize the CFL in hyperbolic-shaped microchannels to separate RBCs from plasma. For this purpose, we have investigated the effect of hyperbolic contractions on the CFL by using not only different Hencky strains but also varying the series of contractions. The results show that the hyperbolic contractions with a Hencky strain of 3 and higher, substantially increase the CFL downstream of the contraction region in contrast with the microchannels with a Hencky strain of 2, where the effect is insignificant. Although, the highest CFL thickness occur at microchannels with a Hencky strain of 3.6 and 4.2 the experiments have also shown that cells blockage are more likely to occur at this kind of microchannels. Hence, the most appropriate hyperbolic-shaped microchannels to separate RBCs from plasma is the one with a Hencky strain of 3.The authors acknowledge the financial support provided by PTDC/SAU-ENB/116929/2010 and EXPL/EMS-SIS/2215/2013 from FCT (Fundação para a Ciência e a Tecnologia), COMPETE, QREN and European Union (FEDER). R.O. Rodrigues, D. Pinho and P. C. Sousa acknowledge the scholarships SFRH/BD/97658/2013, SFRH/BD/89077/2012 and SFRH/BPD/75258/2010, respectively, all attributed by FCT

Blood flow visualization and measurements in microfluidic devices fabricated by a micromilling technique

The most common and used technique to produce microfluidic devices for biomedical applications is the soft-lithography. However, this is a high cost and time-consuming technique. Recently, manufacturers were able to produce milling tools smaller than 100 m and consequently have promoted the ability of the micromilling machines to fabricate microfluidic devices capable of performing cell separation. In this work, we show the ability of a micromilling machine to manufacture microchannels down to 30 m and also the ability of a microfluidic device to perform partial separation of red blood cells from plasma. Flow visualization and measurements were performed by using a high-speed video microscopy system. Advantages and limitations of the micromilling fabrication process are also presented.The authors acknowledge the financial support provided by PTDC/SAU-ENB/116929/2010 and EXPL/EMS-SIS/ 2215/2013 from FCT (Science and Technology Foundation), COMPETE, QREN and European Union (FEDER). DP acknowledge the PhD scholarship SFRH/BD/89077/2012, and P.C. Sousa acknowledges the fellowship SFRH/BPD/75258/ 2010, all attributed by FCT.info:eu-repo/semantics/publishedVersio

Laser-Induced Fluorometry for Capillary Electrophoresis

Laser-induced fluorometry (LIF) has achieved the detection of single molecules, which ranks it among the most sensitive of detection techniques, whereas capillary electrophoresis (CE) is known as a powerful separation method with resolution that is beyond the reach of many other types of chromatography. Therefore, a coupling of LIF with CE has established an unrivaled analytical technique in terms of sensitivity and resolution. CE-LIF has demonstrated excellent performance in bioanalytical chemistry for the high-resolution separation and highly sensitive detection of DNAs, proteins, and small bioactive molecules. This review describes the CE-LIF methods developed by the author's group that include indirect and direct detection using diode lasers, post-column derivatization, and Hadamard transformation, as well as applications to the binding assays of specific DNA immunoassays of proteins and to the determination of anticancer drugs

A transient helix in the disordered region of dynein light intermediate chain links the motor to structurally diverse adaptors for cargo transport

All animal cells use the motor cytoplasmic dynein 1 (dynein) to transport diverse cargo toward microtubule minus ends and to organize and position microtubule arrays such as the mitotic spindle. Cargo-specific adaptors engage with dynein to recruit and activate the motor, but the molecular mechanisms remain incompletely understood. Here, we use structural and dynamic nuclear magnetic resonance (NMR) analysis to demonstrate that the C-terminal region of human dynein light intermediate chain 1 (LIC1) is intrinsically disordered and contains two short conserved segments with helical propensity. NMR titration experiments reveal that the first helical segment (helix 1) constitutes the main interaction site for the adaptors Spindly (SPDL1), bicaudal D homolog 2 (BICD2), and Hook homolog 3 (HOOK3). In vitro binding assays show that helix 1, but not helix 2, is essential in both LIC1 and LIC2 for binding to SPDL1, BICD2, HOOK3, RAB-interacting lysosomal protein (RILP), RAB11 family-interacting protein 3 (RAB11FIP3), ninein (NIN), and trafficking kinesin-bind-ing protein 1 (TRAK1). Helix 1 is sufficient to bind RILP, whereas other adaptors require additional segments preceding helix 1 for efficient binding. Point mutations in the C-terminal helix 1 of Caenorhabditis elegans LIC, introduced by genome editing, severely affect development, locomotion, and life span of the animal and disrupt the distribution and transport kinetics of membrane cargo in axons of mechanosensory neurons, identical to what is observed when the entire LIC C-terminal region is deleted. Deletion of the C-terminal helix 2 delays dynein-dependent spindle positioning in the one-cell embryo but overall does not significantly perturb dynein function. We conclude that helix 1 in the intrinsically disordered region of LIC provides a conserved link between dynein and structurally diverse cargo adaptor families that is critical for dynein function in vivo.This work was financed by the Fundo Europeu de Desenvolvimento Regional (FEDER) through the Norte Portugal Regional Operational Programme (NORTE 2020), Portugal 2020 (RG); by the Fundação para a Ciência e a Tecnologia (FCT)/Ministério da Ciência, Tecnologia e Ensino Superior in the framework of the project NORTE-01-0145-FEDER-030507 (RG); by FCT fellowships IF/01015/2013/CP1157/CT0006 (RG) and SFRH/ BPD/101898/2014 (DJB); by the European Research Council under the European Union’s Seventh Framework Programme, ERC grant agreement no. ERC-2013-StG-338410-DYNEINOME (RG), and by a start-up package of the University of Colorado (BV). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript