Recruitment of single human low-threshold motor units with increasing loads at different muscle lengths

We investigated the recruitment behaviour of low threshold motor units in flexor digitorum superficialis by altering two biomechanical constraints: the load against which the muscle worked and the initial muscle length. The load was increased using isotonic (low load), loaded dynamic (intermediate load) and isometric (high load) contractions in two studies. The initial muscle position reflected resting muscle length in series A, and a longer length with digit III fully extended in series B. Intramuscular EMG was recorded from 48 single motor units in 10 experiments on five healthy subjects, 21 units in series A and,27 in series B, while subjects performed ramp up, hold and ramp down contractions. Increasing the load on the muscle decreased the force, displacement and firing rate of single motor units at recruitment at shorter muscle lengths (P < 0.001, dependent t-test). At longer muscle lengths this recruitment pattern was observed between loaded dynamic and isotonic contractions, but not between isometric and loaded dynamic contractions. Thus, the recruitment properties of single motor units in human flexor digitorum superficialis are sensitive to changes in both imposed external loads and the initial length of the muscle. (C) 2003 Elsevier Ltd. All rights reserved.

Anharmonic effects on a phonon-number measurement of a quantum-mesoscopic-mechanical oscillator

We generalize a proposal for detecting single-phonon transitions in a single nanoelectromechanical system (NEMS) to include the intrinsic anharmonicity of each mechanical oscillator. In this scheme two NEMS oscillators are coupled via a term quadratic in the amplitude of oscillation for each oscillator. One NEMS oscillator is driven and strongly damped and becomes a transducer for phonon number in the other measured oscillator. We derive the conditions for this measurement scheme to be quantum limited and find a condition on the size of the anharmonicity. We also derive the relation between the phase diffusion back-action noise due to number measurement and the localization time for the measured system to enter a phonon-number eigenstate. We relate both these time scales to the strength of the measured signal, which is an induced current proportional to the position of the read-out oscillator.

Surface modification of metals by calcium carbonate thin films on a layer-by-layer polyelectrolyte matrix

A multilayer organic film containing poly(acrylic acid) and chitosan was fabricated on a metallic support by means of the layer-by-layer technique. This film was used as a template for calcium carbonate crystallization and presents two possible binding sites where the nucleation may be initiated, either calcium ions acting as counterions of the polyelectrolyte or those trapped in the template gel network formed by the polyelectrolyte chains. Calcium carbonate formation was carried out by carbon dioxide diffusion, where CO, was generated from ammonium carbonate decomposition. The CaCO3 nanocrystals obtained, formed a dense, homogeneous, and continuous film. Vaterite and calcite CaCO3 crystalline forms were detected. (c) 2007 Elsevier B.V All rights reserved.

Self-assembled films from WO(3): Electrochromism and lithium ion diffusion

WO(3)/chitosan and WO(3)/chitosan/poly(ethylene oxide) (PEO) films were prepared by the layer-by-layer method. The presence of chitosan enabled PEO to be carried into the self-assembled structure, contributing to an increase in the Li(+) diffusion rate. On the basis of the galvanostatic intermittent titration technique (GITT) and the quadratic logistic equation (QLE), a spectroelectrochemical method was used for determination of the ""optical"" diffusion coefficient (D(op)), enabling analysis of the Li(+) diffusion rate and, consequently, the coloration front rate in these host matrices. The D(op) values within the WO(3)/chitosan/PEO film were significantly higher than those within the WO(3)/chitosan film, mainly for higher values of injected charge. The presence of PEO also ensured larger accessibility to the electroactive sites, in accordance with the method employed here. Hence, this spectroelectrochemical method allowed us to separate the contribution of the diffusion process from the number of accessible electroactive sites in the materials, thereby aiding a better understanding of the useful electrochemical and electrochromic properties of these films for use in electrochromic devices. (C) 2010 Elsevier B.V. All rights reserved.

Refining the perfusion-diffusion mismatch hypothesis

Background and Purpose-The Echoplanar Imaging Thrombolysis Evaluation Trial ( EPITHET) tests the hypothesis that perfusion-weighted imaging (PWI)-diffusion-weighted imaging (DWI) mismatch predicts the response to thrombolysis. There is no accepted standardized definition of PWI-DWI mismatch. We compared common mismatch definitions in the initial 40 EPITHET patients. Methods-Raw perfusion images were used to generate maps of time to peak (TTP), mean transit time (MTT), time to peak of the impulse response (Tmax) and first moment transit time (FMT). DWI, apparent diffusion coefficient ( ADC), and PWI volumes were measured with planimetric and thresholding techniques. Correlations between mismatch volume (PWIvol-DWIvol) and DWI expansion (T2(Day) (90-vol)-DWIAcute-vol) were also assessed. Results-Mean age was 68 +/- 11, time to MRI 4.5 +/- 0.7 hours, and median National Institutes of Health Stroke Scale (NIHSS) score 11 (range 4 to 23). Tmax and MTT hypoperfusion volumes were significantly lower than those calculated with TTP and FMT maps (P < 0.001). Mismatch >= 20% was observed in 89% (Tmax) to 92% (TTP/FMT/MTT) of patients. Application of a +4s ( relative to the contralateral hemisphere) PWI threshold reduced the frequency of positive mismatch volumes (TTP 73%/FMT 68%/Tmax 54%/MTT 43%). Mismatch was not significantly different when assessed with ADC maps. Mismatch volume, calculated with all parameters and thresholds, was not significantly correlated with DWI expansion. In contrast, reperfusion was correlated inversely with infarct growth (R= -0.51; P = 0.009). Conclusions-Deconvolution and application of PWI thresholds provide more conservative estimates of tissue at risk and decrease the frequency of mismatch accordingly. The precise definition may not be critical; however, because reperfusion alters tissue fate irrespective of mismatch.

Interfacial interactions and structure of organic-inorganic nanohybrids

Understanding the interfacial interactions and structure is important to better design and application of organic-inorganic nanohybrids. This paper presents our recent molecular dynamic studies on organoclays and polymer nanocomposites, including the layering behavior of organoclays, structural and dynamic properties of dioctadecyldimethyl ammoniums in organoclays, and interfacial interactions and structure of polyurethane nanocomposites. The results demonstrate that the layering behaviors of organoclays are closely related to the chain length of quaternary alkyl ammoniums and cation exchangeable capacity of clays. In addition to typical layered structures such as monolayer, bilayer and pseudo-trilayer, a pseudo-quadrilayer structure was also observed in organoclays modified with dioctadecyldimethyl ammoniums (DODDMA). In such a structure, alkyl chains do not lie flat within a single layer but interlace, and also jump to the next layer or even the next nearest layer. Moreover, the diffusion constants of nitrogen and methylene atoms increase with the temperature and methelene towards the tail groups. For polyurethane nanocomposite, the van der Waals interaction between apolar alkyl chains and soft segments of polyurethane predominates the interactions between organoclay and polyurethane. Different from most bulk polyurethane systems, there is no distinct phase-separated structure for the polyurethane.

The states, diffusion, and concentration distribution of water in radiation-formed PVA/PVP hydrogels

Hydrogels with various compositions of polyvinyl alcohol (PVA) and poly(1-vinyl-2-pyrrolidinone) (PVP) were prepared by irradiating mixtures of PVA and PVP in aqueous solutions with gamma-rays from Co-60 sources at room temperature. The states of water in the hydrogels were characterized using DSC and NMR T-2 relaxation measurements and the kinetics of water diffusion in the hydrogels were studied by sorption experiments and NMR imaging. The DSC endothermic peaks in the temperature range -10 to +10 degrees C implied that there are at least two kinds of freezable water present in the matrix. The difference between the total water content and the freezable water content was refer-red to as bound water, which is not freezable. The weight fraction of water at which only nonfreezable water is present in a hydrogel with F-VP = 0.19 has been estimated to be g(H2O)/g(Polymer) = 0.375. From water sorption experiments, it was demonstrated that the early stage of the diffusion of water into the hydrogels was Fickian. A curve-fit of the early-stage experimental data to the Fickian model allowed determination of the water diffusion coefficient, which was found to lie between 1.5 x 10(-11) m(2) s(-1) and 4.5 x 10(-11) m(2) s(-1), depending on the polymer composition, the cross-link density, and the temperature. It was also found that the energy barrier for diffusion of water molecules into PVA/PVP hydrogels was approximate to 24 kJ mol(-1). Additionally, the diffusion coefficients determined from NMR imaging of the volumetric swelling of the gels agreed well with the results obtained by the mass sorption method.

Double diffusion-driven convective instability of three-dimensional fluid-saturated geological fault zones heated from below

We conduct a theoretical analysis to investigate the double diffusion-driven convective instability of three-dimensional fluid-saturated geological fault zones when they are heated uniformly from below. The fault zone is assumed to be more permeable than its surrounding rocks. In particular, we have derived exact analytical solutions to the total critical Rayleigh numbers of the double diffusion-driven convective flow. Using the corresponding total critical Rayleigh numbers, the double diffusion-driven convective instability of a fluid-saturated three-dimensional geological fault zone system has been investigated. The related theoretical analysis demonstrates that: (1) The relative higher concentration of the chemical species at the top of the three-dimensional geological fault zone system can destabilize the convective flow of the system, while the relative lower concentration of the chemical species at the top of the three-dimensional geological fault zone system can stabilize the convective flow of the system. (2) The double diffusion-driven convective flow modes of the three-dimensional geological fault zone system are very close each other and therefore, the system may have the similar chance to pick up different double diffusion-driven convective flow modes, especially in the case of the fault thickness to height ratio approaching 0. (3) The significant influence of the chemical species diffusion on the convective instability of the three-dimensional geological fault zone system implies that the seawater intrusion into the surface of the Earth is a potential mechanism to trigger the convective flow in the shallow three-dimensional geological fault zone system.

Study of acetylcholinesterase activity in rectal suction biopsy for diagnosis of intestinal dysganglionoses: 17-year experience of a single center

Although the utility of the acetylcholinesterase (AChE) histochemistry on rectal suction biopsy in diagnosing Hirschsprung`s disease (HD) has been documented, few reports address a great number of biopsies and patients. Our aim is to present a 17-year experience on the method of rectal suction biopsy and AChE histochemical staining for diagnosis of intestinal dysganglionoses. Between August 1989 and July 2006, 297 children suspected of having HD were submitted to rectal suction biopsies that were evaluated by the same two surgeons. There were 18 complications (6.0%), namely one self-limited rectal bleeding and 17 (5.7%) inadequate procedures that were repeated. A total of 157 patients (52.8%) showed no increased AChE activity and the remaining patients (140-47.2.0%) presented patterns of increased AChE activity confirming the diagnosis of HD or neuronal intestinal dysplasia. Among the 140 cases suspected as having HD, in 131 children the diagnosis of HD was confirmed and they were operated on. The histological studies showed that 111 children presented the classic form of HD or a long spastic segment. Sixteen children presented total colonic aganglionosis and four children proved to have intestinal neuronal dysplasia, according to histological and radiological criteria. Nine (6.6%) newborns were identified as false-positives and no false-negative results were verified. The rectal suction biopsy combined with AChE staining is advantageous for the differentiation between normal bowel and intestinal dysganglionoses. The rectal suction method is simple and can easily be performed by experienced surgeons. The histological evaluation is very objective and can be performed by a non-pathologist.

Axial Young's modulus prediction of single-walled carbon nanotube arrays with diameters from nanometer to meter scales

Based on a self-similar array model, we systematically investigated the axial Young's modulus (Y-axis) of single-walled carbon nanotube (SWNT) arrays with diameters from nanometer to meter scales by an analytical approach. The results show that the Y-axis of SWNT arrays decreases dramatically with the increases of their hierarchy number (s) and is not sensitive to the specific size and constitution when s is the same, and the specific Young's modulus Y-axis(s) is independent of the packing configuration of SWNTs. Our calculations also show that the Y-axis of SWNT arrays with diameters of several micrometers is close to that of commercial high performance carbon fibers (CFs), but the Y-axis(s) of SWNT arrays is much better than that of high performance CFs. (C) 2005 American Institute of Physics.

Acute Toxic Leukoencephalopathy: Potential for Reversibility Clinically and on MRI With Diffusion-Weighted and FLAIR Imaging

OBJECTIVE. Toxic leukoencephalopathy may present acutely or subacutely with symmetrically reduced diffusion in the periventricular and supraventricular white matter, hereafter referred to as periventricular white matter. This entity may reverse both on imaging and clinically. However, a gathering together of the heterogeneous causes of this disorder as seen on MRI with diffusion-weighted imaging (DWI) and an analysis of their likelihood to reverse has not yet been performed. Our goals were to gather causes of acute or subacute toxic leukoencephalopathy that can present with reduced diffusion of periventricular white matter in order to promote recognition of this entity, to evaluate whether DWI with apparent diffusion coefficient (ADC) values can predict the extent of chronic FLAIR abnormality ( imaging reversibility), and to evaluate whether DWI can predict the clinical outcome ( clinical reversibility). MATERIALS AND METHODS. Two neuroradiologists retrospectively reviewed the MRI examinations of 39 patients with acute symptoms and reduced diffusion of periventricular white matter. The reviewers then scored the extent of abnormality on DWI and FLAIR. ADC ratios of affected white matter versus the unaffected periventricular white matter were obtained. Each patient`s clinical records were reviewed to determine the cause and clinical outcome. Histology findings were available in three patients. Correlations were calculated between the initial MRI markers and both the clinical course and the follow-up extent on FLAIR using Spearman`s correlation coefficient. RESULTS. Of the initial 39 patients, seven were excluded because of a nontoxic cause (hypoxic-ischemic encephalopathy [HIE] or congenital genetic disorders) or because of technical errors. In the remaining 32 patients, no correlation was noted between any of the initial MRI markers (percentage of ADC reduction, DWI extent, or FLAIR extent) with the clinical outcome. Three patients had histologic correlation. However, moderate correlation was seen between the extent of abnormality on initial FLAIR and the extent on follow-up FLAIR (r = 0.441, p = 0.047). Of the 13 patients who underwent repeat MRI at 21 days or longer, the reduced diffusion resolved in all but one. Significant differences were noted between ADC values in affected white matter versus unaffected periventricular white matter on initial (p < 0.0001) but not on follow-up MRI (p = 0.13), and in affected white matter on initial versus follow-up (p = 0.0014) in those individuals who underwent repeat imaging on the same magnet (n = 9), confirming resolution of the DWI abnormalities. CONCLUSION. Acute toxic leukoencephalopathy with reduced diffusion may be clinically reversible and radiologically reversible on DWI, and may also be reversible, but to a lesser degree, on FLAIR MRI. None of the imaging markers measured in this study appears to correlate with clinical outcome, which underscores the necessity for prompt recognition of this entity. Alerting the clinician to this potentially reversible syndrome can facilitate treatment and removal of the offending agent in the early stages.