Small Bath Research Articles

Quantum many-body theory of qubit decoherence in a finite-size spin bath. II. Ensemble dynamics

Decoherence of a center spin or qubit in a spin bath is essentially determined by the many-body bath evolution. The bath dynamics can start either from a pure state or, more generally, from a statistical ensemble. In the preceding article [W. Yang and R. B. Liu, Phys. Rev. B 78, 085315 (2008)], we developed the cluster-correlation expansion (CCE) theory for the so-called single-sample bath dynamics initiated from a factorizable pure state. Here we present the ensemble CCE theory, which is based on similar ideas of the single-sample CCE. The bath evolution is factorized into the product of all possible cluster correlations, each of which accounts for the authentic (nonfactorizable) collective excitation of a group of bath spins and for the finite-time evolution in the qubit decoherence problem. Convergent results can be obtained by truncating the ensemble CCE by keeping cluster correlations up to a certain size. A difference between the ensemble CCE and single-sample CCE is that the mean-field treatment in the latter formalism of the diagonal part of the spin-spin interaction in the bath is not possible in the former case. The ensemble CCE can be applied to nonfactorizable initial states. The ensemble CCE is checked against the exact solution of an $XY$ spin bath model. For small spin baths, it is shown that single-sample dynamics is sensitive to the sampling of the initial state from a thermal ensemble and hence very different from the ensemble average.

Funktionelle Untersuchungen von Ionenkanälen in unmyelinisierten Axonen des Menschen

Clinical assessment of large fibre neuropathy is a routine neurological procedure. The clinical assessment of small fibre function however is far less well established and as a consequence pharmaceutical therapies for small fibre neuropathies often comprise sequential trials with different medications until one works. To refine the diagnosis and treatment of small fibre neuropathies a fuller understanding of the physiological and pharmacological profile of human unmyelinated axons is required. To this end we have adopted the in vitro preparation of human sural nerve segments first described by Lambert and Dyck (1) and developed techniques to examine the excitability and chemosensitivity of human unmyelinated axons. Individual nerve fascicles were extracted from sural nerve segments taken at biopsy or after amputation and mounted between stimulating and recording suction electrodes in a small organ bath. The excitability of all unmyelinated axons within an individual fascicle was determined by monitoring the amplitude and latency of the compound C fibre action potential response to constant current electrical stimulation. Using threshold tracking techniques it is possible to monitor multiple excitability parameters (2) of human C-fibres during the application of pharmacological agents to the bathing solution. We have used this in vitro preparation to examine the effect of specific inflammatory mediators on the excitability of human C fibres as well as the ability of several compounds used in the clinical treatment of neuropathic pain to influence the effects of such mediators.

Quantum many-body theory of qubit decoherence in a finite-size spin bath

Decoherence of a center spin or qubit in a spin bath is essentially determined by the many-body bath evolution. We develop a cluster-correlation expansion (CCE) theory for the spin-bath dynamics relevant to the qubit decoherence problem. A cluster-correlation term is recursively defined as the evolution of a group of bath spins divided by the cluster correlations of all the subgroups. This correlation accounts for the authentic (nonfactorizable) collective excitations within a given group. The bath propagator is the product of all possible cluster correlation terms. For a finite-time evolution as in the qubit decoherence problem, a convergent result can be obtained by truncating the expansion up to a certain cluster size. The two-spin cluster truncation of the CCE corresponds to the pair-correlation approximation developed previously [W. Yao et al., Phys. Rev. B 74, 195301 (2006)]. In terms of the standard linked cluster expansion, a cluster-correlation term is the infinite summation of all the connected diagrams with all and only the spins in the group flip-flopped, and thus the expansion is exact whenever convergence occurs. When the individual contribution of each higher-order correlation term to the decoherence is small (while all the terms combined in product could still contribute substantially), as the usual case for relatively large baths, where the decoherence could complete well within the bath spin flip-flop time, the CCE coincides with the cluster expansion [W. M. Witzel and S. Das Sarma, Phys. Rev. B 74, 035322 (2006)]. For small baths, however, the qubit decoherence may not complete within the bath spin flip-flop time scale and thus individual higher-order cluster correlations could become significant. In such cases, only the CCE converges to the exact coherent dynamics of multispin clusters. We check the accuracy of the CCE in an exactly solvable spin-chain model.

Long-time electron spin storage via dynamical suppression of hyperfine-induced decoherence in a quantum dot

The coherence time of an electron spin decohered by the nuclear spin environment in a quantum dot can be substantially increased by subjecting the electron to suitable dynamical decoupling sequences. We analyze the performance of high-level decoupling protocols by using a combination of analytical and exact numerical methods, and by paying special attention to the regimes of large interpulse delays and long-time dynamics, which are outside the reach of standard average Hamiltonian theory descriptions. We demonstrate that dynamical decoupling can remain efficient far beyond its formal domain of applicability, and find that a protocol exploiting concatenated design provides best performance for this system in the relevant parameter range. In situations where the initial electron state is known, protocols able to completely freeze decoherence at long times are constructed and characterized. The impact of system and control nonidealities is also assessed, including the effect of intrabath dipolar interaction, magnetic field bias and bath polarization, as well as systematic pulse imperfections. While small bias field and small bath polarization degrade the decoupling fidelity, enhanced performance and temporal modulation result from strong applied fields and high polarizations. Overall, we find that if the relative errors of the control pulse flip angles do not exceed 3%, decoupling protocols can still prolong the coherence time by up to 2 orders of magnitude.

Nonlinear Microrheology: Bulk Stresses versus Direct Interactions

In passive microrheology, the linear viscoelastic properties of complex fluids are inferred from the Brownian motion of colloidal tracer particles. Active (but gentle) forcing may also be used to obtain such linear-response information. More significant forcing may drive the material significantly out of equilibrium, thus potentially providing a window into the nonlinear response properties of the material. In leaving the linear-response regime, however, the theoretical underpinning for passive microrheology is lost, and a variety of issues arise. Most generally, what exactly can be measured, and how can such measurements be interpreted? Here we motivate and discuss a variety of theoretical issues facing the interpretation of active microrheology. First, in the continuum limit, the inhomogeneous velocity field around the probe gives rise to rheological inhomogeneities, whereupon an assumed generalized Stokes drag yields a weighted average of the viscosities around the probe rather than the (homogeneous) viscosity measured macroscopically. We then explicitly treat the material microstructure using a model system (a large colloidal probe pulled through a dilute suspension of small bath particles). We examine the different sources of stress upon the probe particle (e.g., direct probe-bath collisions as well as microstructural deformations within the bulk suspension) and discuss their analog (or lack thereof) in the corresponding macrorheological system. We discuss several crucial issues for the interpretation of nonlinear microrheology: (1) how to interpret the inhomogeneous and nonviscometric nature of the deformation field around the probe, (2) the distinction between direct and bulk stresses and their deconvolution, and (3) the (Lagrangian) time-dependent nature of the stress histories experienced by material elements as they advect past the probe. Having identified these issues, we briefly discuss adaptations of the basic technique to recover bulk rheology more faithfully. Whereas we specifically discuss a model colloidal suspension, we ultimately envision a technique capable of measuring the nonlinear rheology of general materials.

On the microscopic basis of Newton’s law of cooling and beyond

The microscopic basis of Newton's law of cooling and its modification when the difference in temperature between the system and the surroundings is very large is discussed. When the system of interest is interacting with a small bath, the effect of the dynamical evolution of the bath variables is important to find out its dynamical feedback on the system. As in the usual system-bath approach, however, the bath is finally considered to be in thermal equilibrium and thereby provides an effective generalization of the Born-Markov master equation. It is shown that the cooling at early time is faster than that predicted by Newton's law due to the dynamical feedback of the bath.

Automated fast perfusion of Xenopus oocytes for drug screening

Fast ('concentration jump') applications of neurotransmitters are crucial for screening studies on ligand-gated ion channels. In this paper, we describe a method for automated fast perfusion of neurotransmitters (or drugs) during two-microelectrode voltage-clamp experiments on Xenopus oocytes. The oocytes are placed in a small bath chamber that is covered by a glass plate with two channels for the microelectrodes that are surrounded by a quartz funnel serving as a reservoir for test solutions. The oocytes are perfused in a vertical direction via the two channels in the plate. Automation of compound delivery is accomplished by means of a programmable pipetting workstation. A mean rise time for 10-90% current increase through muscle-type nACh channels of 55.0+/-1.3 ms (30 muM acetylcholine) was estimated. Automation, fast perfusion rates, and economical use of compounds ( approximately 100 mul/data point) make the system suitable for screening studies on ligand- and voltage-gated ion channels.

Galangin protects pig detrusor nerves from repetitive field stimulation and anoxia/glucopenia injury

ObjectivesTo test the capability of the flavonoid galangin to protect pig urinary bladder from damage due to a period of repetitive field stimulation as well as a period of anoxia/glucopenia and reperfusion. MethodsSmooth muscle strips of the pig bladder were mounted for tension recording in small organ baths and the strips underwent either 1.5 hours of repetitive field stimulation at 32 Hz for 15 seconds every 5 minutes or under anoxia/glucopenia and reperfusion conditions. Galangin, at different concentrations, was added to the reperfusion Krebs solution to check the effect of this flavonoid compared with untreated strips under the same conditions. A group of experiments was performed to examine its possible underlying mechanisms. ResultsRepetitive field stimulation for 1.5 hours caused a progressive decrease in the maximal contractile response to electrical field stimulation (34% decrease). Galangin (10−7 M) partially prevented the progressive decrease in the contractile response. This effect was significantly reduced when verapamil was added to the solution. Galangin significantly improved the response of strips to electrical field stimulation under anoxia/glucopenia and reperfusion conditions compared with untreated tissues. ConclusionsGalangin has a protective effect on bladder contractility by an action that at least, in part, depends on l-type calcium channels. Furthermore, galangin protects detrusor nerves against the anoxia/glucopenic and reperfusion damage.

Influence of Solvent-Solvent and Solute-Solvent Interaction Propertieson Solvent-Mediated Potential**The project supported by National NaturalScience Foundation of China under Grant No. 20206033

A recently proposed universal calculational recipe for solvent-mediatedpotential is applied to calculate excess potential of mean force between twolarge Lennard–Jones (LJ) or hard core attractive Yukawa particles immersedin small LJ solvent bath at supercritical state. Comparison between thepresent prediction with a hypernetted chain approximation adopted forsolute-solute correlation at infinitely dilute limit and existing simulationdata shows high accuracy for the region with large separation, andqualitative reliability for the solute particle contact region. Thecalculational simplicity of the present recipe allows for a detailedinvestigation on the effect of the solute-solvent and solvent-solventinteraction details on the excess potential of mean force. The resultantconclusion is that gathering of solvent particles near a solute particleleads to repulsive excess PMF, while depletion of solvent particles awayfrom the solute particle leads to attractive excess PMF, and minor change of thesolvent-solvent interaction range has large influence on the excess PMF.

Development of Mass Production of Ce0.9Gd0.1O1.95 Nanopowder with High-Sintering Characteristics

The mass production process of Ce0.9Gd0.1O1.95 (CGO) nanopowder with high-sintering characteristics has been studied. Although CGO powders were fabricated using a large scale coprecipitation bath with a capacity of 65 kg/batch, particle size distribution curve of this powder showed two peaks for the agglomeration and this powder showed lower sintering characteristics, compared to the CGO nanopowder by a small scale bath with a capacity of 0.1 kg/batch. It was found that when the impurity of NO3 - in the powder was removed by water using the rate of 50 L/kg, the formation of oval shape particles was observed and it is easy to crush the agglomerations in the powder by hammer-type mill. The sintering characteristics of this powder are almost same to those of the powder synthesized by the small scale bath.

Economical helium bath cryopump: design and testing

A small UHV helium bath cryopump with low cryoliquid consumption has been designed, manufactured and tested. The cryopump is designed to keep UHV in electron optical devices without generation of disturbing electromagnetic fields or vibrations. The outer volume of its shell is 15 l, the filling volumes of liquid helium (LHe) and liquid nitrogen (LN 2) are 3.0 l and 3.4 l, respectively. Operating times between cryoliquid fillings are 35 days for LHe and 6 days for LN 2. A pump speed of 25 l/s was measured for the He gas. A lowest pressure of 1.5×10 −7 Pa was achieved in a test chamber and the pumping tests indicated that an even lower pressure would be achieved in a well-degassed chamber. Good agreement between the calculated and measured values both of the pump speed and the cryoliquid evaporation has been found. The system of chevron-type baffles was designed and checked by Monte Carlo simulations of molecular flow and radiative heat transfer. The pump prototype was successfully used to evacuate an operating cryostat of a NMR spectrometer.

Preconditioning protects the guinea-pig urinary bladder against ischaemic conditions in vitro.

To investigate the ability of ischaemic preconditioning (IPC) to protect guinea-pig detrusor from damage caused by a subsequent more prolonged exposure to ischaemic conditions. Smooth muscle strips were mounted for tension recording in small organ baths continuously superfused with Krebs' solution at 37 degrees C. Ischaemia was mimicked by removing oxygen and glucose from the superfusing solution. Contractile responses to electrical field stimulation (EFS) and carbachol were monitored. Three regimes of preconditioning were examined: 15, 10, and 5 min of ischaemic conditions followed by 15, 10, and 5 min of normal conditions, respectively. Without preconditioning, nerve-mediated responses were significantly and proportionally reduced by periods of ischaemic conditions lasting for 45, 60, and 90 min, but recovered fully after exposure to ischaemic conditions for 30 min. The recovery of the responses to EFS was significantly improved in preconditioned strips when the period of ischaemic conditions was 45 or 60 min. However, no significant differences were seen with preconditioning when the period of ischaemic conditions was 90 min. The recovery of responses to carbachol was much greater than for the responses to EFS, and no significant differences were found between control and preconditioned strips. It is suggested that in vivo short periods of transient ischaemia may be able to protect the guinea-pig bladder from the impairment associated with longer periods of ischaemia and reperfusion, which might happen in obstructed micturition. Our results also indicate that the phenomenon affects mainly the intrinsic nerves, which are more susceptible to ischaemic damage than the smooth muscle.

Barrier Crossing Coupled to a Small Set of Oscillators

This paper presents a study of the behavior of a one-dimensional system, with two potential minima separated by a barrier, coupled to a small set of harmonic oscillators. The time correlation function of equilibrium fluctuations in particle number (number correlation function) is found by computer simulation. An analogue of Kramers turnover in the barrier crossing rate is observed. The Grote−Hynes theory of non-Markovian rate processes provides a reasonable estimate for the rate constant at intermediate frictions. However, at high friction, the number correlation function becomes nonexponential, and the decay is much slower than expected from the Grote−Hynes theory. The model shows that close coupling to a small heat bath provides a mechanism for “internal friction”.

Small helium bath cryopump for electron optical devices

A small helium bath cryopump for electron optical devices has been designed and manufactured. The filling volumes of LHe and LN2 are 2.5 and 3.6 l, respectively. Special electron beam welding methods were utilised for the pump structure. The heat loads of the cryogens were minimised using numerical methods. An LHe refill interval of 30 days was reached, whereas that of LN2 is 6 days. Good agreement between the calculated and measured values has been found. An ultimate pressure of 3×10 −7 Pa and a pumping speed better than that of a comparable ion pump were reached during a preliminary testing of pumping properties.

Neuroprotection afforded by some hindered phenols and alpha-tocopherol in guinea-pig detrusor strips subjected to anoxia-glucopenia and reperfusion-like conditions.

2-t-butyl-4-methoxyphenol (BHA), 3,5-di-t-butyl-hydroxyanisole (DTBHA), 2,6-diisopropylphenol (propofol), alpha-tocopherol (alpha-TOC) and two newly synthesised analogues of BHA, namely 1-O-(4-hydroxy-3-t-butyl)phenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranose (beta-TAG) and 1-O-(4-hydroxy-3-t-butyl)phenyl-beta-D-glucopyranose (beta-GLU), were tested for their capability to protect the intrinsic nerves of guinea-pig urinary bladder from damage due to anoxia-glucopenia and re-exposure to glucose and O2. Guinea-pig detrusor strips were mounted for tension recording in small organ baths, superfused with warmed Krebs solution and the nerves stimulated electrically either under control or ischaemia-like (anoxia-glucopenia) and reperfusion-like conditions (normal medium re-superfusion). The Ca2+ antagonist activity of the compounds was assessed by their effect on the contraction of detrusor strips induced by 60 mM K+ Krebs solution in the presence of either 0.5 mM or 5 mM Ca2+. The antioxidant activity was illustrated by the ability of the compounds to scavenge peroxyl radicals generated by linoleic acid oxidation. All the compounds, except beta-GLU and alpha-TOC, inhibited in a concentration-dependent manner K+-induced contractions of detrusor muscles, the inhibition being inversely related to the Ca2+ concentration of the perfusion solution; moreover, they exhibited a marked antiperoxidant activity with pIC50 values decreasing in the order: DTBHA > alpha-TOC > BHA > beta-TAG > propofol > beta-GLU. alpha-TOC, BHA, DTBHA and beta-TAG improved significantly the response of the strips to electrical field stimulation either during the anoxia-glucopenia phase or thereafter when recovering during reperfusion, as compared to untreated tissues. The neuroprotection afforded by the phenol derivatives as well as by alpha-TOC was positively correlated to their antioxidant activity, but not to their Ca2+ antagonist activity.

Vasoactive intestinal peptide protects guinea-pig detrusor nerves from anoxia/glucopenia injury

Vasoactive intestinal peptide (VIP) was tested for its capability to protect the intrinsic nerves of guinea-pig urinary bladder from damage due to anoxia/glucopenia and reperfusion. Guinea-pig detrusor strips were mounted for tension recording in small organ baths and the nerves were subjected to electric field stimulation. VIP (0.3 μM) improved significantly the response of strips to electrical field stimulation either during anoxia/glucopenia or thereafter during reperfusion, as compared to untreated tissues. The antioxidant activity of VIP assessed as its capability to scavenge peroxyl radicals during linoleic acid oxidation corresponded to 6.42±0.13 pIC 50 M, i.e. close to the concentration proved to protect strips against the anoxic–glucopenic and reperfusion damage.

The Big Freeze: Water and the Scientific Process

In recent years there has been increasing movement toward laboratory exercises that are inquiry-based, requiring students to assume more active roles in the learning process. A laboratory experiment was developed in this light, framed around a simple question, “Which freezes faster, hot water or cold water?” The experiment was used at the beginning of the general chemistry year-long course sequence and served as an introduction to the scientific process. Students were each asked to develop a hypothesis and then design a simple experiment to determine which freezes faster, hot water or cold water, using small cold baths to freeze the water. A strength of this experiment is that students not only design and perform the experiments, but at the end they evaluate each other’s methods.

Risk of hydrocyanic acid release in the electroplating industry

This paper suggests assessing the consequences of hydrocyanic acid (HCN) release into the air by aqueous cyanide solutions in abnormal situations such as the accidental introduction of an acid, or the insertion of a cyanide in a pickling bath. It provides a well-defined source model and its resolution by methods peculiar to mass transport phenomena. The procedure consists of four stages: calculation of the liquid phase concentration, estimate of the HCN liquid–vapour equilibrium, determination of the mass transfer coefficient at the liquid–vapour interface, evaluation of the air concentration of HCN and of the damage distances. The results show that small baths operating at high temperatures are the major sources of risk. The building up of lethal air concentrations, on the other hand, is governed by the values of the mass transfer coefficient, which is itself determined by the flow dynamics and bath geometry. Concerning the magnitude of the risk, the fallout for external emergency planning is slight in all the cases investigated.

Grignard Reactions in "Wet" Ether

A small laboratory ultrasonic bath can be used to initiate the Grignard reaction of alkyl or aryl bromides in regular laboratory-quality, undried, diethyl ether and in simple undried test tubes. The reaction typically starts within 30 to 45 seconds and is self-sustaining. Yields and products are the same as obtained with carefully dried ether and equipment. We normally run this reaction at the 1.5-gram scale, but the procedure can be scaled up to at least 10 g of the bromide.

A flash vaporizing flow calorimeter for the measurement of enthalpy increments. Test measurements onn-hexane atT = 473.2 K andT = 510.2 K and pressures up top = 5.2 MPa

A new design of flow calorimeter for the measurement of enthalpy increments is reported. The novel feature is that the calorimeter is a flash vaporizer mounted in a small bath of heated silicone oil. Cold liquid pumped into the calorimeter is vaporized and electrical energy supplied to the oil-bath is adjusted by a computer to ofset exactly the incremental enthalpy change and maintain the oil at a constant temperature. The apparatus is designed to operate over the temperature rangeT= 240 K to T= 523 K at pressures up top= 10 MPa. A measurement of the incremental enthalpy change can be made in 30 min. Test measurements on n -hexane at pressures up to p= 5.2 MPa have been made in the liquid and gaseous regions at the temperature T= 473.2 K, and in the supercritical region atT= 510.2 K. The accuracy of the measurements is ± 2 per cent.