Electrocardiogram derived respiration during sleep

The aim of this study was quantify the ECG Derived Respiration (EDR) in order to extend the capabilities of ECG-based sleep analysis. We examined our results in normal subjects and in patients with Obstructive Sleep Apnea Syndrome (OSAS) or Central Sleep Apnea. Lead 2 ECG and three measures of respiration (thorax and abdominal effort, and oronasal flow signal) were recorded during sleep studies of 12 normal and 12 OSAS patients. Three parameters, the R-wave amplitude (RWA), R-wave duration (RWD), and QRS area, were extracted from the ECG signal, resulting in time series that displayed a behavior similar to that of the respiration signals. EDR frequency was correlated with directly measured respiratory frequency, and averaged over all subjects. The peak-to-peak value of the EDR signals during the apnea event was compared to the average peak-to-peak of the sleep stage, containing the apnea. 1

Electronic Structure of Lanthanum Hydrides with Switchable Optical Properties

Recent dramatic changes in the optical properties of LaH_{2+x} and YH_{2+x} films discovered by Huiberts et al. suggest their electronic structure is described best by a local model. Electron correlation is important in H^- -centers and in explaining the transparent insulating behavior of LaH_3. The metal-insulator transition at $x\sim 0.8$ takes place in a band of highly localized states centered on the $H$-vacancies in the LaH_3 structure.Comment: plain tex, 3 figure

Design of high-magnetic field gradient sources for controlling magnetically induced flow of ferrofluids in microfluidic systems

The use of miniature electromagnets for ferrofluid-actuated liquid dispensing into microfluidic channels has been investigated by numerical simulations using the finite element method and measurements of fluid displacement and flow rate. The simulations illustrate the effect of structural and geometrical parameters of single and paired solenoid coils on the magnetic force experienced by the ferrofluid. Dual solenoids were used for extended fluid displacement. Ferrofluid positioning and flow rates were controlled also by using a solenoid with an iron core. The experimental measurements of fluidflow in capillaries were used to validate the modeling calculations. The results can be used as a basis for the development of on-chip ferrofluid-based devices integrated with microfluidic architectures

Microelectromagnetic ferrofluid-based actuator

Computer simulations were used to investigate the performance of a microscale ferrofluid-based magnetic actuator developed for liquid dispensing in microfluidic channels. The actuation was based on the movement of a ferrofluid plug in a magnetic field gradient generated by on-chip effectively infinite parallel conductors. The movement, positioning, and retaining of ferrofluid plugs with different lengths at various locations along a microfluidic channel were investigated for two cases. In case (a), the magnetic field gradient was generated by a single conductor; when the ferrofluid reached its equilibrium position, the current was switched off and the nearest neighbor conductor was energized. A similar, consecutive on/off current switching was performed for case (b), where a set of conductors was energized simultaneously

Electroluminescence-detected magnetic-resonance study of polyparaphenylenevinylene (PPV)-based light-emitting diodes

The strong electroluminescence (EL)-detected magnetic resonance of PPV-based light emitting diodes is compared to the conductivity (sigma)- and photoluminescence (PL)-detected resonances. It provides direct evidence that polaron-to-singlet exciton conversion is responsible for the EL. In contrast to the narrow PL-enhancing resonance assigned to polaron recombination, strong EL- and sigma-quenching resonances are attributed to the spin-dependent polaron-to-bipolaron decay. The half-field EL- and sigma-detected resonances of two distinct triplet excitons is believed to result from triplet-triplet fusion to singlets

Robust Signal Processing in Living Cells

Cellular signaling networks have evolved an astonishing ability to function reliably and with high fidelity in uncertain environments. A crucial prerequisite for the high precision exhibited by many signaling circuits is their ability to keep the concentrations of active signaling compounds within tightly defined bounds, despite strong stochastic fluctuations in copy numbers and other detrimental influences. Based on a simple mathematical formalism, we identify topological organizing principles that facilitate such robust control of intracellular concentrations in the face of multifarious perturbations. Our framework allows us to judge whether a multiple-input-multiple-output reaction network is robust against large perturbations of network parameters and enables the predictive design of perfectly robust synthetic network architectures. Utilizing the Escherichia coli chemotaxis pathway as a hallmark example, we provide experimental evidence that our framework indeed allows us to unravel the topological organization of robust signaling. We demonstrate that the specific organization of the pathway allows the system to maintain global concentration robustness of the diffusible response regulator CheY with respect to several dominant perturbations. Our framework provides a counterpoint to the hypothesis that cellular function relies on an extensive machinery to fine-tune or control intracellular parameters. Rather, we suggest that for a large class of perturbations, there exists an appropriate topology that renders the network output invariant to the respective perturbations

Strong negative self regulation of Prokaryotic transcription factors increases the intrinsic noise of protein expression

Background Many prokaryotic transcription factors repress their own transcription. It is often asserted that such regulation enables a cell to homeostatically maintain protein abundance. We explore the role of negative self regulation of transcription in regulating the variability of protein abundance using a variety of stochastic modeling techniques. Results We undertake a novel analysis of a classic model for negative self regulation. We demonstrate that, with standard approximations, protein variance relative to its mean should be independent of repressor strength in a physiological range. Consequently, in that range, the coefficient of variation would increase with repressor strength. However, stochastic computer simulations demonstrate that there is a greater increase in noise associated with strong repressors than predicted by theory. The discrepancies between the mathematical analysis and computer simulations arise because with strong repressors the approximation that leads to Michaelis-Menten-like hyperbolic repression terms ceases to be valid. Because we observe that strong negative feedback increases variability and so is unlikely to be a mechanism for noise control, we suggest instead that negative feedback is evolutionarily favoured because it allows the cell to minimize mRNA usage. To test this, we used in silico evolution to demonstrate that while negative feedback can achieve only a modest improvement in protein noise reduction compared with the unregulated system, it can achieve good improvement in protein response times and very substantial improvement in reducing mRNA levels. Conclusions Strong negative self regulation of transcription may not always be a mechanism for homeostatic control of protein abundance, but instead might be evolutionarily favoured as a mechanism to limit the use of mRNA. The use of hyperbolic terms derived from quasi-steady-state approximation should also be avoided in the analysis of stochastic models with strong repressors

Theory for Metal Hydrides with Switchable Optical Properties

Recently it has been discovered that lanthanum, yttrium, and other metal hydride films show dramatic changes in the optical properties at the metal-insulator transition. Such changes on a high energy scale suggest the electronic structure is best described by a local model based on negatively charged hydrogen (H$^-$) ions. We develop a many-body theory for the strong correlation in a H$^-$ ion lattice. The metal hydride is described by a large $U$-limit of an Anderson lattice model. We use lanthanum hydride as a prototype of these compounds, and find LaH$_3$ is an insulator with a substantial gap consistent with experiments. It may be viewed either as a Kondo insulator or a band insulator due to strong electron correlation. A H vacancy state in LaH$_3$ is found to be highly localized due to the strong bonding between the electron orbitals of hydrogen and metal atoms. Unlike the impurity states in the usual semiconductors, there is only weak internal optical transitions within the vacancy. The metal-insulator transition takes place in a band of these vacancy states.Comment: 18 pages, 16 figures and 6 tables. Submitted to PR

Interobserver Agreement in the Diagnosis of Stroke Type

Interobserver Agreement is Essential to the Reliability of Clinical Data from Cooperative Studies and Provides the Foundation for Applying Research Results to Clinical Practice. in the Stroke Data Bank, a Large Cooperative Study of Stroke, We Sought to Establish the Reliability of a Key Aspect of Stroke Diagnosis: The Mechanism of Stroke. Seventeen Patients Were Evaluated by Six Neurologists. Interobserver Agreement Was Measured When Diagnosis Was based on Patient History and Neurologic Examination Only, as Well as When It Was based on Results of a Completed Workup, Including a Computed Tomographic Scan. Initial Clinical Impressions, based Solely on History and One Neurologic Examination, Were Fairly Reliable in Establishing the Mechanism of Stroke (Ie, Distinguishing among Infarcts, Subarachnoid Hemorrhages, and Parenchymatous Hemorrhages). Classification into One of Nine Stroke Subtypes Was Substantially Reliable When Diagnoses Were based on a Completed Workup. Compared with Previous Findings for the Same Physicians and Patients, the Diagnosis of Stroke Type Was Generally More Reliable Than Individual Signs and Symptoms. These Results Suggest that Multicentered Studies Can Rely on the Independent Diagnostic Choices of Several Physicians When Common Definitions Are Employed and Data from a Completed Workup Are Available. Furthermore, Reliability May Be Less for Individual Measurements Such as Signs or Symptoms Than for More-Complex Judgments Such as Diagnoses. © 1986, American Medical Association. All Rights Reserved