Mixture Of Spikes Research Articles

Development and comparison of two high accuracy methods for uranium concentration in nuclear fuel: ID-TIMS and K-edge densitometry

This study compares the two analytical methods for uranium concentration determination with high accuracy in uranium pellet: K-edge densitometer (KED) and the isotope dilution with thermal ionisation mass spectrometry measurements (ID-TIMS). Both techniques are compared in terms of time, generated radioactive effluent, simplicity, uncertainty estimation and detection limit. ID-TIMS shows lower detection limit and uncertainties than KED. However, the KED analysis time is shorter and generates less effluent. Both techniques were used for metrological analysis of uranium concentration in nuclear materials. The optimization of sample spike mixture isotope ratio for ID-TIMS to decrease uncertainties is also discussed.

A novel sample loading method and protocol for monitoring sample fractionation for high precision Ca stable isotope ratio measurements using double-spike TIMS

The external reproducibility (2σSD) of Ca stable isotope ratio measurements (δ44/40Ca) using double-spike (43Ca–48Ca) thermal ionization mass spectrometry (TIMS) is better than 0.08 ‰ using our proposed loading technique.

A Robust Procedure for High‐Precision Determination of Rare Earth Element Concentrations in Seawater

This study reports a robust procedure that permits precise measurement of all fourteen naturally occurring rare earth element (REE) concentrations, present at ng kg−1 to sub ng kg−1 levels, in ~ 100 ml seawater. This procedure is simple and can be routinely applied to measure seawater REEs with relatively high sample throughput. The procedure involves addition of a 142Ce‐145Nd‐171Yb‐enriched spike mixture, iron co‐precipitation, REE purification with chromatographic separation and the use of a magnetic‐sector‐field ICP‐MS (Element 2) coupled with a desolvating sample introduction system (Aridus 1). Critical steps of the procedure, including co‐precipitation pH and matrix removal, have been optimised through a set of experiments described here. The accuracy of the new procedure was assessed against a gravimetric mixture of REEs, and the precision was demonstrated by repeated measurement of two well‐mixed natural seawaters. Repeated analyses of these seawater reference materials (RMs), using ~ 100 ml seawater for each aliquot, indicate precision of 3% (1s) for the REEs. Measured REE concentrations of two uncertified seawater RMs (CASS‐4 and NASS‐5) are consistent with published values, and REE concentrations of the GEOTRACES intercalibration samples show good agreement with those reported by other participant laboratories. REE concentrations for other intercalibration samples (SAFe and Arctic PS70) are also reported.

Models for Forecasting the Demand and Supply of Electricity in Nigeria

In this paper, the Garch model is used to determine the market volatility in the demand and supply chains of electricity in Nigeria for 36 years, i.e. from 1970 to 2005 from the historic data obtained from the National Bureau of Statistics. The Harvey logistic model is used to predict the demand and supply of electricity in the country from 2005 to 2026. From the results obtained, the demand and supply of electricity show mixture of spikes because of mean reverse behavior about the mean values and the demand outweighed the supply. The consequence of this is that there is vast market prosperity for investors in the power sector in Nigeria. It is estimated that about 317.5 billion US dollars business opportunities are available to new independent power stations in Nigeria.

Spike sorting of heterogeneous neuron types by multimodality-weighted PCA and explicit robust variational Bayes.

This study introduces a new spike sorting method that classifies spike waveforms from multiunit recordings into spike trains of individual neurons. In particular, we develop a method to sort a spike mixture generated by a heterogeneous neural population. Such a spike sorting has a significant practical value, but was previously difficult. The method combines a feature extraction method, which we may term “multimodality-weighted principal component analysis” (mPCA), and a clustering method by variational Bayes for Student's t mixture model (SVB). The performance of the proposed method was compared with that of other conventional methods for simulated and experimental data sets. We found that the mPCA efficiently extracts highly informative features as clusters clearly separable in a relatively low-dimensional feature space. The SVB was implemented explicitly without relying on Maximum-A-Posterior (MAP) inference for the “degree of freedom” parameters. The explicit SVB is faster than the conventional SVB derived with MAP inference and works more reliably over various data sets that include spiking patterns difficult to sort. For instance, spikes of a single bursting neuron may be separated incorrectly into multiple clusters, whereas those of a sparsely firing neuron tend to be merged into clusters for other neurons. Our method showed significantly improved performance in spike sorting of these “difficult” neurons. A parallelized implementation of the proposed algorithm (EToS version 3) is available as open-source code at http://etos.sourceforge.net/.

Determination of Priority Polybrominated Diphenyl Ethers by Isotope Dilution Gas Chromatography(Electron Ionization)MS Using 81Br-Labeled Standards

A mixture of (81)Br-labeled polybrominated diphenyl ethers (PBDEs), previously synthesized in our laboratory, was separated by liquid chromatography for the individual isolation of different (81)Br-labeled PBDEs containing from 3 to 6 bromine atoms. The different fractions were collected, and a mixed labeled standard was then prepared adequate for the determination of priority PBDEs (congeners 28, 47, 99, 100, 153, and 154) in environmental samples. The spike mixture was then characterized using gas chromatography(electron ionization)MS (GC(EI)MS) both in isotope composition and concentration in combination with multiple least-squares. Contamination from natural abundance BDEs 153 and 154 was detected in the spike mixture, and a new isotope dilution equation was developed to take into account the natural abundance contribution from the spike. The spike mixture was shown to be stable during at least 4 months, and no isotope exchange between natural abundance and labeled PBDEs was detected during this period of time. Finally, the (81)Br-labeled PBDEs standard was used for the determination of congeners 28 (+33), 47, 49, 99, 100, 153, and 154 in a standard reference material (Lake Michigan fish tissue SRM 1947) using three different sample to spike ratios. No methodological calibration needed to be prepared, as no isotopic effects were detected using this labeling mode. Concentrations found were in agreement with the certified concentrations (recoveries between 89% and 116%), and reproducibility was always below 7% RSD. Kragten procedure was used to calculate expanded uncertainties. Very low limits of detection were obtained for all compounds (between 0.02 and 0.9 ng·g(-1)) using the procedure developed here.

Mixed mode oscillations in a gonadotropin-releasing hormone (GnRH) neuron model

Mixed mode oscillations (MMOs) are complex patterns resulting from an inter-mixing of large- and smallamplitude oscillations. Such patterns have been widely observed in experiments as well as mathematical models [1] and are currently an active area of mathematical research. In neurons MMOs often consist of a mixture of spikes and subthreshold oscillations. Our GnRH work leads to a seven-dimensional soma model aimed at investigating the firing properties of GnRH neurons across puberty. The results of our model are supported by published electrophysiological data of Liu and Herbison [2]. The model exhibits robust subthreshold oscillations in addition to action potentials, an observation validated by experimental evidence. Previously identified mechanisms giving rise to MMOs in mathematical models include canard-based mechanisms such as folded node singularities and singular Hopf bifurcations [3,4]. MMOs arising out of these mechanisms have characteristic patterns of variation in oscillation amplitudes; in the case of folded nodes there are also bounds for the maximum number of subthreshold oscillations per cycle. The MMOs in our system do not follow these patterns but are instead “exotic” MMOs. In this work we use geometric singular perturbation theory to analyze the source of these MMOs in the model and compare to known mechanisms; we also explore the possible physiological function of MMOs in GnRH cells. Bifurcation analysis of our system was performed with the help of the simulation and continuation tool XPPAUT. Our analysis suggests that MMOs in our model persist near a saddle-node of periodic orbits and the geometry further points to a tangency between an unstable manifold and a family of periodic orbits. In order to facilitate a more detailed analysis of this phenomenon we reduced to a three dimensional fastslow system with two slow variables that exhibits qualitatively similar MMOs. We note here that MMOs in three or higher dimensional systems have been observed to occur robustly when two of the variables evolve on a much slower time-scale than the rest [3-5] unlike in two dimensional systems where they occur over an exponentially small parameter interval. The bifurcation analysis of our reduced model provides insights into the geometry of stable and unstable invariant manifolds of our system and their role in the generation of the exotic MMOs.

Synthesis of 81Br-Labeled Polybrominated Diphenyl Ethers and Their Characterization Using GC(EI)MS and GC(ICP)MS

A mixture of different (81)Br-labeled polybrominated diphenyl ethers (PBDEs) was prepared and characterized for its future use as spike for the isotope dilution analysis of PBDEs. The synthesis was carried out by direct bromination of diphenyl ether using (81)Br enriched Br(2) obtained after aqueous oxidation of bromide with potassium peroxymonosulfate and extraction into dichloromethane. The number of bromine atoms introduced in the diphenyl ether molecule depended on the molar ratio between bromine and diphenyl ether. The final mixture prepared contained a mixture of tri-, tetra-, penta-, and hexabrominated PBDEs with a larger concentration of the tetrabrominated congener BDE-47. The isotopic composition of bromine in the resulting PBDEs mixture was determined by GC(ICP)MS and resulted in a 99.53% enrichment of the isotope 81 of bromine. The concentration of three of the PBDE congeners (28, 47, and 99) in the mixture was determined by reverse isotope dilution analysis using a certified, natural abundance, PBDEs mixture and both GC(ICP)MS and GC(EI)MS. For this purpose, the fragmentation and isotope distribution patterns of the different PBDE cogeners in the positive electron ionization source were studied in detail both for natural abundance and labeled compounds. A procedure based on isotope pattern deconvolution was developed which allowed the direct determination of the concentration of the labeled PBDEs in the spike mixture by GC(EI)MS. Finally, the GC(EI)MS isotope pattern deconvolution procedure was applied for the determination of natural abundance congeners 28, 47, and 99 in spiked waters at ng L(-1) levels. Detection limits below 0.5 ng L(-1) could be obtained for all compounds using only 100 mL of sample and liquid-liquid extraction with isooctane.

Inference algorithms and learning theory for Bayesian sparse factor analysis

Bayesian sparse factor analysis has many applications; for example, it has been applied to the problem of inferring a sparse regulatory network from gene expression data. We describe a number of inference algorithms for Bayesian sparse factor analysis using a slab and spike mixture prior. These include well-established Markov chain Monte Carlo (MCMC) and variational Bayes (VB) algorithms as well as a novel hybrid of VB and Expectation Propagation (EP). For the case of a single latent factor we derive a theory for learning performance using the replica method. We compare the MCMC and VB/EP algorithm results with simulated data to the theoretical prediction. The results for MCMC agree closely with the theory as expected. Results for VB/EP are slightly sub-optimal but show that the new algorithm is effective for sparse inference. In large-scale problems MCMC is infeasible due to computational limitations and the VB/EP algorithm then provides a very useful computationally efficient alternative.

Canards, Clusters, and Synchronization in a Weakly Coupled Interneuron Model

Applying a low current to a recent biophysical model for inhibitory neurons in the cortex leads to mixed mode oscillations (MMOs), a mixture of spikes and subthreshold oscillations. At higher currents, the neurons fire regularly. We show that a specific slow potassium current underlies this behavior. Next we reduce this five-dimensional biophysical model for an inhibitory neuron to three dimensions with a slow/fast time-scale structure. We then show that there is a range of parameters under which the reduced model shows MMOs which can be explained by the canard phenomenon. Many inhibitory interneurons are coupled with electrical tight junctions (gap junctions). We show that such coupling combined with the underlying MMOs produces clustered solutions in large networks. We explain this using the theory of weakly coupled oscillators and show that the complex dynamics arises from sensitivity near the canard.

Sleep Spindles Mixed with Spikes. Any Clinical Significance?

ABSTRACT.Spikes are commonly found in association with K complexes in patients with primary generalized epilepsy. A mixture of spikes and (unusually abundant) sleep spindles, however, is rather unique in clinical EEG. Such a blend of spikes and spindles was the hallmark of a sleep tracing in a 10-year-old boy with recent onset of seizures. Seizure type and the waking EEG suggested frontal (especially left frontal) origin of the seizures. The history and clinical findings revealed a mild encephalopathy, presumably caused by prematurity and associated with a moderate type of autism. Computed tomography (CT) findings were unremarkable. The combination of frontal lobe epilepsy with mixed spindles and spikes is not readily understood and deserves attention. The overabundance of spindles could be related to the pattern known as “extreme spindles.”

Lidocaine‐Dependent Early Infantile Epileptic Encephalopathy with Hyponatremia and Highly Suppressed EEG

Purpose: Early infantile epileptic encephaiopathy with suppression burst (EIEE) is characterized by an EEG pattern that alternates between an irregular mixture of spikes and waves and almost flat activity, each lasting from 1 to several seconds. This report presents a case characterized by lidocaine dependence, intractable hyponatremia, and an EEG pattern that alternates between extremely long suppression and short burst. In addition, the possible pathomechanism of the suppression is discussed.Case report; We examined a female patient born at term by normal delivery, who had a birth weight of 2,546 g and a head circumference of 33 cm. She did not present with asphyxia but hardly cried artd was unable to breast feed. Blood studies showed persistent hyponatremia ranging between 120 and 130 mEq/L. Endocrinological examinations disclosed no abnormalities. Despite NaCl loading and water restriction, the persistent hyponatremia did not show improvement. Tube feeding was started, but her activity and responsiveness remained poor. One month after birth, clonic seizures were observed in the face and limbs. Phenobarbital and diazepam were only transiently effective. Valproate and vitamin B6 were ineffective. Ten days after the onset of seizures, the patient was transferred to our hospital. On admission, she demonstrated repeated seizure activity every 1 to 2 minutes, lasting 10 to 15 seconds. Movement consisted of a series of tonic extension of the upper limbs, head turning toward the right, and clonic right hemiconvulsion. The head circumference increased to 41 cm at one and half month. The EEG showed burst activity during the seizure movements and suppressed flat activity during the interictal phase lasting I to 2 minutes. There were no spontaneous movements other than seizure and no response even to noxious stimuli. After starting intravenous lidocaine administration, the seizure activity improved and completely disappeared within 8 hours. The next day, the patient was able to cry and her hyponatremia improved. Three days after starting lidocaine, she was able to breast feed and the duration of the suppression phase in the EEG decreased to less than 10 seconds. Within several hours of ceasing lidocaine administration, the seizure movements reappeared and the EEG showed an extremely suppressed pattern. Within a several hours after restarting lidocaine, seizure movements disappeared, and the EEG improved. Based on these observations, we continued intravenous administration of lidocaine at a serum concentration of approximately 0.5 y/ml. Thereafter, head circumference improved, the EEG changed from a suppression burst pattern to an irregular slow wave pattern, and the patient showed more development, Nevertheless, an MRI revealed progressive cerebral atrophy. We changed from intravenous administration of lidocaine to the viscous lidocaine to enable administration through a gastric tube.Given the pharmacological mechanisms of lidocaine as a sodium channel blocker, we speculate that our patient had a sodium channel dysfunction that caused an overflow of sodium from the extracellular apace into neurons and other excitable cells. This hypothesis could explain the characteristic findings in our patient including intractable hyponatremia, extremely suppressed EEG, and subacute megalencephaly. We believe that this mechanisms merits further consideration.

Studies of field emission current from amorphous silicon deposited on a tungsten tip

Field electron emission from an amorphous silicon deposited tungsten tip has been studied. The current–voltage ( I– V) characteristics corresponding to the as-deposited and annealed states of the emitter were recorded. These characteristics showed semiconducting behaviour. Field emission current fluctuations from the two states were recorded. As-deposited tip shows more spikes in low-field region and a mixture of spikes and steps at higher fields. Fast Fourier Transform analysis of the current signal shows Lorentzian-type of power spectrum which is indicative of bistable traps in a-Si : H. Total emission current level remained almost constant for the entire duration of recording.

Cardiazol賦活による犬の脳波

Cardiazol activated electroencephalograms (EEG) were recorded from four normal dogs. The relationship between clinical features and the appearance of signs of electroencephalographic abnormality was investigated. The EEG seizures were a mixture of spikes, slow waves, and spike-and-slow-wave complexes in the early stage of Cardiazol activation. Following this spike-and-slow-wave complex phase, the EEG revealed persistent and generalized spikes (grand mal phase) and thereafter revealed an inactive phase (resting phase). Clinical manifestations of the seizures consisted of tonic flexion, tonic extension, and clonic convulsion. These motor seizures were in association with changes in the EEG seizures. A typical change in activities of the brain was observed by power spectral analysis. It was concluded that cardiazol activation was a useful technique for reproducing epileptic seizures, and that the activated EEG examination was also useful for clinical diagnosis in epileptic dogs.

A precise and accurate method for the quantitative determination of carbonate minerals by X-Ray diffraction using a spiking technique

SummaryA precise and accurate X-ray diffraction method has been developed whereby the weight percentages of aragonite and low- and high-magnesium calcite are determined from the integrated peak areas of spiked and unspiked samples. The spike mixture was prepared from organisms extracted from the samples to be analysed. Use of a spiking method also avoided the preparation of working curves from artificial mixtures of carbonate minerals, which may not have the same diffraction behaviour as the unknowns. A test of the precision of the method indicates the following coefficients of variation: aragonite, 1·4 %; low-magnesium calcite, 1·5 %; high-magnesium calcite, 7·8 %. A test of the accuracy of the method indicates no significant bias in any of the carbonate results, except in samples where high-magnesium calcite values are below 10 %. Quartz may also be determined by this method (coefficient of variation 23·9 %; positive bias in values greater than 10 %).