387 research outputs found
Cryogenic Ion Trapping Systems with Surface-Electrode Traps
We present two simple cryogenic RF ion trap systems in which cryogenic
temperatures and ultra high vacuum pressures can be reached in as little as 12
hours. The ion traps are operated either in a liquid helium bath cryostat or in
a low vibration closed cycle cryostat. The fast turn around time and
availability of buffer gas cooling made the systems ideal for testing
surface-electrode ion traps. The vibration amplitude of the closed cycled
cryostat was found to be below 106 nm. We evaluated the systems by loading
surface-electrode ion traps with Sr ions using laser ablation, which
is compatible with the cryogenic environment. Using Doppler cooling we observed
small ion crystals in which optically resolved ions have a trapped lifetime
over 2500 minutes.Comment: 10 pages, 13 EPS figure
Cardiorespiratory synchronization: is it a real phenomenon
Abstract In this work we present a quantitative approach to the analysis of cardiorespiratory synchronization, which is a newly discovered phenomenon. The primary aim of this Introduction Modulation of heart rate (HR) by respiration, which is the main source of heart rate variability, is long known. This phenomenon has been studied extensively, and although it is not fully understood, its physiological determinants have been unveiled. Lately, the study of phase synchronization in chaotic oscillators has led to the discovery of another aspect of cardiorespiratory interaction: synchronization between respiration and HR [I]. Cardiorespiratory synchronization (CS) was observed in young athletes in coexistence with modulation of HR by respiration. The synchronization was found using a novel visualization tool, the Synchrogram [ 11. The Synchrogram enables to visually detect epochs of synchrony between two noisy signals, with any rational frequency ratio. The qualitative analysis of cardiorespiratory interaction presented in [1,2] raises two questions: a) is cardiorespiratory synchronization a real phenomenon, The two questions are related. Associating distinct physiological conditions to CS negates the hypothesis of CS being random. Indeed, preliminary results indicate that CS is associated with lower HR variability, and more specifically, with reduced values of parasympathetic activity [l-21. In this work, we apply the approach of surrogate data analysis to the study of CS, in order to answer the first question. Surrogate data 'analysis is a widely used approach in the field of nonlinear dynamics, especially when trying to assess a functional relation between an attribute of a system to one of its features. The essence of surrogate analysis is the construction of a (surrogate) data set from the original data, while preserving all features of the data, except for the one whose influence is being tested. A difference in the measured attribute between the real and surrogate data then indicates that it is related to that specific feature that is absent in the surrogates. Our analysis relates the heart-respiration coupling to the synchronization between them. The surrogates were constructed by considering the interaction between respiration and heart rate taken from different subjects. Avoiding randomization of the signals themselves, as commonly done in surrogate data analysis, preserves all features of the cardiorespiratory system, except for the coupling between the two subsystems. We applied a previously developed algorithm, which enables to quantify CS [3], to the analysis of the real and surrogate data. We then compared the statistical properties of the observed CS in both real and surrogate data. Our results show that synchronization appears in both real and surrogate data, although significantly less in the surrogates. Cardiorespiratory synchronization should therefore enter the cadre of cardiorespiratory interactions. Unveiling its physiological determinants and relating cardiorespiratory pathologies to CS will undoubtedly increase our knowledge of this complex system
Trion induced negative photoconductivity in monolayer MoS2
Optical excitation typically enhances electrical conduction and low-frequency
radiation absorption in semiconductors. We have, however, observed a pronounced
transient decrease of conductivity in doped monolayer molybdenum disulfide
(MoS2), a two-dimensional (2D) semiconductor, under femtosecond laser
excitation. In particular, the conductivity is reduced dramatically down to
only 30% of its equilibrium value with high pump fluence. This anomalous
phenomenon arises from the strong many-body interactions in the system, where
photoexcited electron-hole pairs join the doping-induced charges to form
trions, bound states of two electrons and one hole. The resultant increase of
the carrier effective mass substantially diminishes the carrier conductivity
Validity of the Polar V800 heart rate monitor to measure RR intervals at rest
Purpose To assess the validity of RR intervals and short-term heart rate variability (HRV) data obtained from the Polar V800 heart rate monitor, in comparison to an electrocardiograph (ECG). Method Twenty participants completed an active orthostatic test using the V800 and ECG. An improved method for the identification and correction of RR intervals was employed prior to HRV analysis. Agreement of the data was assessed using intra-class correlation coefficients (ICC), Bland–Altman limits of agreement (LoA), and effect size (ES). Results A small number of errors were detected between ECG and Polar RR signal, with a combined error rate of 0.086 %. The RR intervals from ECG to V800 were significantly different, but with small ES for both supine corrected and standing corrected data (ES 0.999 for both supine and standing corrected intervals. When analysed with the same HRV software no significant differences were observed in any HRV parameters, for either supine or standing; the data displayed small bias and tight LoA, strong ICC (>0.99) and small ES (≤0.029). Conclusions The V800 improves over previous Polar models, with narrower LoA, stronger ICC and smaller ES for both the RR intervals and HRV parameters. The findings support the validity of the Polar V800 and its ability to produce RR interval recordings consistent with an ECG. In addition, HRV parameters derived from these recordings are also highly comparable
Multifractality in Human Heartbeat Dynamics
Recent evidence suggests that physiological signals under healthy conditions
may have a fractal temporal structure. We investigate the possibility that time
series generated by certain physiological control systems may be members of a
special class of complex processes, termed multifractal, which require a large
number of exponents to characterize their scaling properties. We report on
evidence for multifractality in a biological dynamical system --- the healthy
human heartbeat. Further, we show that the multifractal character and nonlinear
properties of the healthy heart rate are encoded in the Fourier phases. We
uncover a loss of multifractality for a life-threatening condition, congestive
heart failure.Comment: 19 pages, latex2e using rotate and epsf, with 5 ps figures; to appear
in Nature, 3 June, 199
Dynamics of trimming the content of face representations for categorization in the brain
To understand visual cognition, it is imperative to determine when, how and with what information the human brain categorizes the visual input. Visual categorization consistently involves at least an early and a late stage: the occipito-temporal N170 event related potential related to stimulus encoding and the parietal P300 involved in perceptual decisions. Here we sought to understand how the brain globally transforms its representations of face categories from their early encoding to the later decision stage over the 400 ms time window encompassing the N170 and P300 brain events. We applied classification image techniques to the behavioral and electroencephalographic data of three observers who categorized seven facial expressions of emotion and report two main findings: (1) Over the 400 ms time course, processing of facial features initially spreads bilaterally across the left and right occipito-temporal regions to dynamically converge onto the centro-parietal region; (2) Concurrently, information processing gradually shifts from encoding common face features across all spatial scales (e.g. the eyes) to representing only the finer scales of the diagnostic features that are richer in useful information for behavior (e.g. the wide opened eyes in 'fear'; the detailed mouth in 'happy'). Our findings suggest that the brain refines its diagnostic representations of visual categories over the first 400 ms of processing by trimming a thorough encoding of features over the N170, to leave only the detailed information important for perceptual decisions over the P300
Characterization of Sleep Stages by Correlations of Heartbeat Increments
We study correlation properties of the magnitude and the sign of the
increments in the time intervals between successive heartbeats during light
sleep, deep sleep, and REM sleep using the detrended fluctuation analysis
method. We find short-range anticorrelations in the sign time series, which are
strong during deep sleep, weaker during light sleep and even weaker during REM
sleep. In contrast, we find long-range positive correlations in the magnitude
time series, which are strong during REM sleep and weaker during light sleep.
We observe uncorrelated behavior for the magnitude during deep sleep. Since the
magnitude series relates to the nonlinear properties of the original time
series, while the signs series relates to the linear properties, our findings
suggest that the nonlinear properties of the heartbeat dynamics are more
pronounced during REM sleep. Thus, the sign and the magnitude series provide
information which is useful in distinguishing between the sleep stages.Comment: 7 pages, 4 figures, revte
ОЦЕНКА РИСКА ОСЛОЖНЕНИЙ ВО ВРЕМЯ ВВОДНОЙ АНЕСТЕЗИИ У ПАЦИЕНТОВ С МАССИВНЫМИ ОПУХОЛЯМИ СРЕДОСТЕНИЯ
Anesthetic management of surgery in patients with large mediastinal mass remains a topical issue of thoracic anesthesiology, since such patients often develop superior mediastinal compression (SMC) which results in a high risk of hemodynamic and respiratory disorders during induction. The degree of compression does not always depend on the mass size, and the prediction of SMC progression during induction becomes a challenge.The method to evaluate the degree of mediastinal compression through the functional orthoclinostatic test was developed – the patient is to be placed in Fowler position for 45 degrees in order to follow changes in the cardiac index.It was found out that the patients with SMC detected during the test (increased cardiac index in Fowler position) had their arterial blood pressure reduced after induction, and the number of critical incidents was statistically significantly higher. The test proved to be a non-invasive and safe method of pre-operative prediction of the risk of SMC development and progression during induction.Анестезиологическое обеспечение оперативных вмешательств у пациентов с массивными опухолями средостения остается актуальной проблемой торакальной анестезиологии, поскольку у больных данной категории заболевание часто осложняется синдромом медиастинальной компрессии (СМК), что приводит к высокому риску гемодинамических и дыхательных нарушений во время вводной анестезии. Степень компрессии не всегда зависит от размеров опухоли, поэтому прогнозирование усугубления СМК во время вводной анестезии остается сложной задачей.Разработали способ оценки степени компрессии средостения методом функциональной ортоклиностатической пробы ‒ перевод пациента в положение Фовлера с наклоном в 45% с определением динамики сердечного индекса.Полученные результаты показали, что у больных с выявленным во время пробы СМК (увеличение сердечного индекса в положении Фовлера) в большей степени происходило снижение артериального давления после вводной анестезии, также было статистически значимо выше количество критических инцидентов. Проба показала себя как неинвазивный и безопасный метод предоперационного прогнозирования риска развития и прогрессирования СМК во время вводной анестезии
- …