Power Dropouts Research Articles

Decoherence and Turbulence Sources in a Long Laser.

We investigate the turn-on process in a laser cavity where the round-trip time is several orders of magnitude greater than the active medium timescales. In this long delay limit, we show that the universal evolution of the photon statistics from thermal to Poissonian distribution involves the emergence of power dropouts. While the largest number of these dropouts vanish after a few round-trips, some of them persist and seed coherent structures similar to dark solitons or Nozaki-Bekki holes described by the complex Ginzburg-Landau equation. These coherent structures connect stationary laser emission domains having different optical frequencies. Moreover, they emit intensity bursts which travel at a different speed, and, depending on the cavity dispersion sign, they may collide with other coherent structures, thus leading to an overall turbulent dynamics. The dynamics is well-modeled by delay differential equations from which we compute the laser coherence time evolution at each round-trip and quantify the decoherence induced by the collisions between coherent structures.

Soft tissue augmentation with a volume-stable collagen matrix or an autogenous connective tissue graft at implant sites: Five-year results of a randomized controlled trial post implant loading.

Interventions to augment the mucosal thickness around dental implants are indicated to optimize esthetics and maintain peri-implant health. However, there is a lack of clinical data on the long-term performance of soft tissue substitutes, such as volume-stable collagen matrix (VCMX), compared to autogenous grafts, such as subepithelial connective tissue grafts (SCTGs). This randomized controlled trial aimed to assess 5-year data on clinical and radiographic outcomes at implant sites previously augmented with VCMX or SCTG. Twenty patients were randomly assigned for soft tissue augmentation with VCMX or SCTG at single implant sites. Following abutment connection, final restorations were inserted (baseline; BL) and patients were reexamined up to 5 years (FU-5). Measurements included clinical data, marginal bone levels, mucosal thickness, and ridge contour changes. Nonparametric tests and estimates were applied for the statistical analysis. The median buccal mucosal thickness increased by 0.3mm (Q1: -0.8; Q3: 1.0) in the VCMX group (P=0.656) and 0.3mm (Q1: 0.0; Q3: 1.0) in the SCTG group (P=0.188) between BL and FU-5 (intergroup P=0.752), while the ridge contour decreased by a median of -0.3mm (-0.9; -0.1) (P=0.078) for VCMX and -0.3mm (-0.4; -0.2) (P=0.039) for SCTG (intergroup P=0.817). Peri-implant health was maintained in both groups with stable clinical and radiographic outcomes and without significant differences between the treatments. Despite the limited power and considerable dropout rate in the present study, soft tissue augmentation at implant sites with either VCMX or SCTG resulted in similar stable peri-implant tissues, favorable esthetics, and clinically negligible contour changes at 5 years post loading.

Turbulent coherent structures in a long cavity semiconductor laser near the lasing threshold

We report on the formation of novel turbulent coherent structures in a long cavity semiconductor laser near the lasing threshold. Experimentally, the laser emits a series of power dropouts within a roundtrip, and the number of dropouts per series depends on a set of parameters including the bias current. At fixed parameters, the drops remain dynamically stable, repeating over many roundtrips. By reconstructing the laser electric field in the case where the laser emits one dropout per roundtrip and simulating its dynamics using a time-delayed model, we discuss the reasons for long-term sustainability of these solutions. We suggest that the observed dropouts are closely related to the coherent structures of the cubic complex Ginzburg-Landau equation.

Chaotic optical power dropouts driven by low frequency bias forcing in a mid-infrared quantum cascade laser

Mid-infrared quantum cascade lasers operating under external optical feedback and external periodic bias forcing are shown to exhibit a deterministic chaotic pattern composed of frequencies which are linked to the one of the forcing. Results also show that both the amplitude and the frequency of the forcing play a key role in the number of retrieved spikes per modulation period. These findings are of paramount importance for chaotic operation of quantum cascade lasers in applications such as optical countermeasure systems and secure atmospheric transmission lines, as well as for simulating neuronal systems and the communication between neurons due to sudden bursts.

Transient electroencephalographic alpha power loss during maintenance of general anaesthesia

BackgroundEEG activity in the extended alpha frequency range (7–17 Hz) during maintenance of general anaesthesia is primarily determined by effect-site concentrations of the hypnotic and analgesic drugs used. Intermittent alpha loss during surgery, unexplained by changes in anaesthetic or opioid concentrations, could represent arousal of the cortex as a result of increased surgical stimulation. MethodsA generalised linear model was fitted to alpha power recorded from patients undergoing general anaesthesia from induction until waking using three explanatory variables: age-adjusted volatile anaesthetic effect-site concentration, and estimated effect-site propofol and opioid concentrations. Model residuals were decomposed into uncorrelated white noise and a fluctuating auto-correlated trend. Deviations of this local trend were classified as ‘unexpected alpha dropout events’. To investigate whether these alpha dropouts might be explained by the effect of noxious stimulation, we related their occurrence to whether a patient was undergoing surgery involving the body cavity or not. ResultsAlpha power dropouts occurred in 73 of the 237 patients included in the final analysis (31%, median amplitude of −3.5 dB, duration=103 s). They showed a bimodal or broadly skewed distribution, being more probable soon after initial incision (32%), dropping to around 10% at 1 h, and then again increasing to >30% in operations lasting >3 h. Multivariate analysis showed that alpha dropouts were significantly associated with body cavity surgery (P=0.003) and with longer operations (P<0.001). ConclusionsA loss of alpha power, unexplained by changes in anaesthetic or opioid concentrations, is suggestive of thalamocortical depolarisation induced by body cavity noxious stimuli, and could provide a measure of nociception during surgery.

Compact standalone platform for neural recording with real-time spike sorting and data logging

Objective. Longitudinal observation of single unit neural activity from large numbers of cortical neurons in awake and mobile animals is often a vital step in studying neural network behaviour and towards the prospect of building effective brain–machine interfaces (BMIs). These recordings generate enormous amounts of data for transmission and storage, and typically require offline processing to tease out the behaviour of individual neurons. Our aim was to create a compact system capable of: (1) reducing the data bandwidth by circa 2 to 3 orders of magnitude (greatly improving battery lifetime and enabling low power wireless transmission in future versions); (2) producing real-time, low-latency, spike sorted data; and (3) long term untethered operation. Approach. We have developed a headstage that operates in two phases. In the short training phase a computer is attached and classic spike sorting is performed to generate templates. In the second phase the system is untethered and performs template matching to create an event driven spike output that is logged to a micro-SD card. To enable validation the system is capable of logging the high bandwidth raw neural signal data as well as the spike sorted data. Main results. The system can successfully record 32 channels of raw neural signal data and/or spike sorted events for well over 24 h at a time and is robust to power dropouts during battery changes as well as SD card replacement. A 24 h initial recording in a non-human primate M1 showed consistent spike shapes with the expected changes in neural activity during awake behaviour and sleep cycles. Significance. The presented platform allows neural activity to be unobtrusively monitored and processed in real-time in freely behaving untethered animals—revealing insights that are not attainable through scheduled recording sessions. This system achieves the lowest power per channel to date and provides a robust, low-latency, low-bandwidth and verifiable output suitable for BMIs, closed loop neuromodulation, wireless transmission and long term data logging.

PERFORMANCE ANALYSIS OF A STEAM TURBINE POWER PLANT AT PART LOAD CONDITIONS

Power consumption highly increases which is related with the growing of the industrial plants and daily using. Increasing power demand can be supplied with building up more efficient plants or optimized old power plants. One of the most important items of a power plant is steam turbine which is designed according to defined parameters (inlet pressure and temperature, flow rates, outlet pressure and power) which also effect the dimensions and performance of the turbine. Turbine loses and irreversibilities are minimum and so efficiencies and power generation are maximum at design conditions. However, power plants always have to operate at off-design or part-load conditions because of the changing of power demands and drop outs of the turbines and other items of the plants. In this study, it is aimed to analyses the isentropic efficiency of a high pressure steam turbine and thermal efficiency of power plant at different load conditions. Analyses showed that both steam turbines and power plant performance were reduced when the power plant operates at partial load conditions.

Low Power Dropout Regulators with Efficiently Controlled Transient Response

Low-Dropout voltage regulators are significant part of VLSI design integrated chips and are used to provide steady supply voltage to noise sensitive analog/RF circuit blocks. It belongs to class of linear regulators designed to minimize the saturation of output pass transistor and its drive requirements. A capacitor-less low-dropout regulator with improved performance push-pull power transistor is described in the paper. The proposed LDO is stable over a wide range of load current and implemented in 65-nm CMOS process technology. The simulation illustrates that the regulator is able to convert VIN of 0.65V- 1.5V to output voltage of 0.5V. This LDO achieves power supply rejection of >40dB at 1 kHz operating frequency. It consumes a quiescent current less than 10 uA. It is capable of delivering a maximum load current of 70 mA with a dropout voltage of less than 220 mV. Keywordsdropout, regulators, low quiescent current, enhanced, capacitor-less.

Low-frequency fluctuations in an external-cavity laser leading to extreme events.

We experimentally investigate the dynamical regimes of a laser diode subject to external optical feedback in light of extreme-event (EE) analysis. We observe EEs in the low-frequency fluctuations (LFFs) regime. This number decreases to negligible values when the laser transitions towards fully developed coherence collapse as the injection current is increased. Moreover, we show that EEs observed in the LFF regime are linked to high-frequency pulsing events observed after a power dropout. Finally, we prove experimentally that the observation of EEs in the LFF regimes is robust to changes in operational parameters.

Characterizing the deterministic nature of individual power dropouts in semiconductor lasers subject to delayed feedback

We implement a method to identify the deterministic nature of specific events in the dynamics of a semiconductor laser subject to time-delayed optical feedback. Specifically, we study the power dropouts in the low-frequency fluctuations regime on an individual event basis and identify whether the underlying dominant mechanism is deterministic. Our approach is based on sychronization with a twin system in a symmetric relay configuration. We investigate the dependence of the fraction of deterministically driven (i.e., synchronized) dropouts on the laser's pump current as a key parameter. Our experimental results are corroborated by numerical modeling based on rate equations. Our numerical findings also provide insights into the influence of spontaneous emission noise.

Experimental control of power dropouts by current modulation in a semiconductor laser with optical feedback

The injection current of an external-cavity semiconductor laser working in a regime of low-frequency fluctuations (LFFs) is modulated at several MHz. The rate of power dropouts in the laser emission is correlated with the amplitude and frequency of the modulating signal. The occurrence of dropouts becomes more regular when the laser is driven at 7 MHz, which is close to the dominant frequency of dropouts in the solitary laser. Driving the laser at 10 MHz also induces dropouts with a periodicity of 0.1 μs, resulting in LFFs with two dominant frequencies.

Expanding Self-Help Imagery Rehearsal Therapy for Nightmares With Sleep Hygiene and Lucid Dreaming: A Waiting-List Controlled Trial

Nightmares are a common disorder with serious consequences. Recently, the cognitive behavioral interventions Imagery Rehearsal Therapy (IRT) and exposure proved effective in a self-help format. The aim of the current study was to compare the following self-help formats to a waiting-list: IRT; IRT with sleep hygiene; and IRT with sleep hygiene and a lucid dreaming section. Two-hundred-seventy-eight participants were included and randomized into a condition. Follow-up measurements were 4, 16, and 42 weeks after baseline. Seventy-three participants filled out all questionnaires and 49 returned the nightmare diaries. Contrary to our expectations, the original IRT was more effective than the two other intervention conditions. Moreover, IRT was the only intervention that convincingly proved itself compared to the waiting-list condition. However, these data should be interpreted with caution due to the low power and high dropout. Yet it seems that in a self-help format, IRT and exposure (which was validated previously) are the treatments of choice for treating nightmares.

Quantifying the statistical complexity of low-frequency fluctuations in semiconductor lasers with optical feedback

Low-frequency fluctuations (LFFs) represent a dynamical instability that occurs in semiconductor lasers when they are operated near the lasing threshold and subject to moderate optical feedback. LFFs consist of sudden power dropouts followed by gradual, stepwise recoveries. We analyze experimental time series of intensity dropouts and quantify the complexity of the underlying dynamics employing two tools from information theory, namely, Shannon's entropy and the Mart\'{\i}n, Plastino, and Rosso statistical complexity measure. These measures are computed using a method based on ordinal patterns, by which the relative length and ordering of consecutive interdropout intervals (i.e., the time intervals between consecutive intensity dropouts) are analyzed, disregarding the precise timing of the dropouts and the absolute durations of the interdropout intervals. We show that this methodology is suitable for quantifying subtle characteristics of the LFFs, and in particular the transition to fully developed chaos that takes place when the laser's pump current is increased. Our method shows that the statistical complexity of the laser does not increase continuously with the pump current, but levels off before reaching the coherence collapse regime. This behavior coincides with that of the first- and second-order correlations of the interdropout intervals, suggesting that these correlations, and not the chaotic behavior, are what determine the level of complexity of the laser's dynamics. These results hold for two different dynamical regimes, namely, sustained LFFs and coexistence between LFFs and steady-state emission.

Assessing the Quality of Evidence From Randomized, Controlled Drug and Nutritional Supplement Trials Conducted Among Nursing Home Residents Between 1968 and 2004: What Can We Learn?

An estimated 1.5 million residents of nursing homes (NH) in the United States were prescribed an average of 7 to 8 medications each month. However, it is unknown which of these prescribed drugs and nutritional supplements have been tested for use among NH residents who often have distinct and complex needs compared with other geriatric patients. This pilot study addresses the quantity and quality of randomized, controlled drug and nutritional supplement trials that have been conducted among NH residents. Using multiple search strategies and review protocol, I assessed the quality of evidence from randomized, controlled drug and nutritional supplement trials that had a parallel-group design, were conducted among NH residents, and were published in English between 1968 and October 2004. Internal validity of the trials was examined by assessing adequately reporting power calculation, drop-outs (completion fraction), randomization and allocation concealment, blind status, and intention-to-treat analysis. External validity of the trials was examined by assessing adequately reporting the sample description, the inclusion and exclusion criteria, the recruitment process, and comorbidities and harm. Relatively few drug and nutritional supplements have been tested among NH residents by well-designed and executed randomized controlled trials (N = 42). The total number of participants (N = 7941) is small. The quality of many trials is poor. Given the limited number and poor quality of existing trials conducted among NH residents in this pilot study, I conclude that there is a limited body of evidence that could be used to establish quality of care standards or pay for performance criteria for drug therapy and nutritional supplements in NH. Long-term care providers face a great challenge in practicing evidence-based medicine in prescribing drugs and nutritional supplements.

Power dropout control by optical phase modulation in a chaotic semiconductor laser

The effect of periodic phase modulation of light on a chaotic external-cavity semiconductor laser working in a regime of low-frequency fluctuations (LFFs) is studied numerically. It is observed that the phase modulation changes the time period between consecutive dropouts in the emitted laser intensity. A new variable ΦL is defined as the phase of the laser's LFFs, which increases in time with 2π after each power dropout event. The phase ΦPM of the periodic phase modulator is unfolded on the real axis and increases linearly at a rate given by the modulating frequency. It is shown that the phase difference between the laser and the modulator ΔΦ(t)=mΦL(t)−nΦPM(t), where m and n are integers, remains constant in time, leading to phase-synchronized states, for specific values of the modulating frequency and amplitude.

Low-frequency fluctuations in two-state quantum dot lasers

We study the feedback-induced instabilities in a quantum dot semiconductor laser emitting in both ground and excited states. Without optical feedback the device exhibits dynamics corresponding to antiphase fluctuations between ground and excited states, while the total output power remains constant. The introduction of feedback leads to power dropouts in the ground state and intensity bursts in the excited state, resulting in a practically constant total output power.

Statistical measures of the power dropout ratio in semiconductor lasers subject to optical feedback

The influence of the optical feedback ratio and bias current on the mean and the standard deviation of the power dropout ratio of low-frequency fluctuations in external-cavity semiconductor lasers has been studied experimentally. The power dropout ratio was found to increase with increasing optical feedback ratio and to decrease with increasing bias current.

Influence of optical feedback time-delay on power-drops in vertical-cavity surface-emitting lasers

The influence of optical feedback time delay on the average period of low-frequency fluctuations (LFF) in external cavity vertical-cavity surface-emitting lasers (VCSELs) is studied experimentally. The regularity of power dropouts is shown to increase with increased external cavity length. Coexistence of LFF and stable operation is observed when the external cavity length is close to the VCSEL coherence length.

The Cassini solar Faraday rotation experiment

The Cassini Faraday rotation experiment improves the current understanding of the coronal magnetic field by making the first measurements of the magnetic field within two solar radii of the south pole and by allowing the separation of the changing electron density from the magnetic field during transient crossings of the line of sight. Simultaneous ranging data to Cassini also contributes to the growing body of empirical electron density models by providing electron density data at solar maximum at varying latitudes including over the poles. Faraday rotation data in the solar corona were collected in 2002 and 2003 using the Cassini spacecraft in cruise to Saturn. Although Cassini primarily transmits in right-hand polarization, enough left-hand is produced to enable polarization measurements. We show that during solar conjunction Faraday rotation is measurable with Cassini. In the X- and Ka-bands both datasets currently show an asymmetric diurnal pattern in polarization not associated with the ionosphere. The Ka-band is much more sensitive to pointing accuracy and experienced periods of power drop outs which caused the left-circularly polarized signal to drop into the noise on occasion during the 2003 conjunction. Interpretation of the dataset is deferred to future papers.

Delay-induced resonances in an optical system with feedback.

We study the influence of the delay time in the response of a delayed feedback system to external periodic driving. The nonlinear system we consider is a semiconductor laser with optical feedback operating in the low-frequency fluctuation regime. We numerically examine the consequences of varying the external cavity length of the system when a weak modulation is introduced through the laser's pump current. The harmonic modulation is seen to lead to a partial periodic entrainment of power dropouts, and the distribution of time intervals between the dropouts exhibits resonances with certain delay times. In other words, the response of the system to the external modulation is enhanced for particular values of the external cavity length. The same effect can be observed in the presence of noise, indicating that stochastic resonance can be enhanced or degraded depending on the feedback time.