Abrupt Decay Research Articles

The Effect of Amorphous Silicon Anode Thickness on the Cycling Behavior of High Energy Density Solid State Li-Ion Batteries

Novel electronic devices related to the internet of things (IoTs) are reshaping our world in several ways. The emergence of these devices is creating an increasing demand for disruptive innovations, among which high performance on-chip integrated energy storage solutions are the most frequently cited. In this regard, thin film batteries (TFBs) are recognized as one of the most propitious electrochemical devices to meet applications’ demands, considering attractive advantages such as excellent cycle life and miniaturization.1,2 Nevertheless, the commercial widespread application of TFBs and the demonstration of effective on-chip integration have been hindered by (i) a low areal energy density and (ii) encapsulation issues related to metallic lithium anode integration. Recently, great efforts have been made to study the interrelationship between materials, architectures, electrochemical performance and integration; the prevailing tendency has been towards Li-free TFBs, where Li anode is formed in-situ during charging. Despite achieving promising electrochemical performance at the full TFB device, significant capacity decay with cycling is usually reported, thus limiting further applications. In the present work, we report on the development of all solid inorganic thin film lithium ion batteries (TFBs) with an amorphous silicon anode solution. The TFBs were realized on 8’’ substrate with a structure integrating a LiCoO2/LiPON/Si active stack (Figure 1.a, inset). The fabrication process flow was carried out in a clean room environment using the TINY platform. The LiCoO2 thickness was kept constant at 20µm whereas several submicron thick silicon anodes were considered (0, 10, 50, 100, 200, 350, and 1000 nm). It was observed no effect of Si anode thickness on the first cycle charge and discharge capacities. Upon cycling, TFBs with the thinnest Si anodes exhibited excellent capacity retention, with an initial discharge capacity of 680µAh.cm-2 and an average loss of 0.1% per cycle. When increasing Si thickness, an abrupt capacity decay was observed at the early stages of cycling, and was correlated to the anode thickness (Fig 1.a). This behavior was correlated to the electrochemical reactions occurring at the anode level: (i) during the first charge, Li ion exchange between LiCoO2 and Si took place, resulting from LiCoO2 delithiation into Li1−xCoO2 and Li−Si alloying. At higher potentials, Li plating occurred at the negative electrode side, and the potential thereby corresponded to that of LiCoO2 vs Li. (ii) during discharge, Li stripping took place at the anode, concomitant with Li ion insertion into Li1−xCoO2. Upon further discharging, Li ion extraction from Li−Si alloys occurred (Fig. 1-b, c). Accordingly, it is concluded that thinner Si films acted as a uniform and homogeneous seed layer to the initial Li plating reaction, thus enhanced the subsequent cycling stability in comparison to Li-free configuration, and thicker Si films lead to severe mechanical delamination within the active stack, and induced TFB capacity decrease (Fig.1-bc). Furthermore, cycling within specific voltage ranges allowed stabilizing the discharge capacity for thicker Si anodes. These results were validated by ToF-SIMS and FIB-SEM characterization. References (1) Lee, H. S.; Kim, S.; Kim, K. B.; Choi, J. W. Scalable Fabrication of Flexible Thin-Film Batteries for Smart Lens Applications. Nano Energy 2018, 53 (August), 225–231. (2) Liu, L.; Weng, Q.; Lu, X.; Sun, X.; Zhang, L.; Schmidt, O. G. Advances on Microsized On-Chip Lithium-Ion Batteries. Small 2017, 13 (45), 1–12. Figure 1

Gravitational Weakening of Seismic Origin as a Driving Mechanism of Some Astronomical Anomalies

The anomalous increase of the astronomical unit, the mysterious secular increase of the lunar eccentricity and the flyby anomaly are important issues of modern astronomy. This study aims to determine the effect of earthquakes on the origin of these anomalies. Based on conventional physics, we found the existence of earthquake-induced gravitational weakening within the earth-moon-sun system and beyond. New equations of gravitation, including time dilation, are introduced that can explain the anomalous increase of the astronomical unit and the lunar orbit. A modified equation that includes the effect of massive quakes also explains the anomalous increase of the lunar eccentricity. Furthermore, the results of the present study can explain the flyby and Pioneer anomalies experienced by spacecraft during gravity assisted maneuvers. A modification of the 3rd Law of Kepler is also presented. Implications on the elliptic orbit of the earth, its reduced velocity and the occurrence of leap years are also discussed. Using the seismic-induced gravitational weakening model, probable trigger mechanisms of the faint young sun paradox and the Allais effect are also presented. An estimate of the age of the earth based on the observed values of the Hubble parameter and the USGS earthquake data for the past century is also presented. A new model of the seismic-driven expanding universe and a new equation to determine the expansion rate of galaxies and the universe is also proposed. The sudden earth’s retreat due to gravitational weakening and its implication on anomalous astronomical refraction and flight risk at night especially near the equatorial region, and its effect on the abrupt satellite orbital decay, spin and drift are also discussed. This study may also shed light on the occurrence of sinkholes and massive landslides. Finally, this study proposes a new equation that can explain the observed changes in the fine structure constant.

Antimony-carbon nanocomposites for potassium-ion batteries: Insight into the failure mechanism in electrodes and possible avenues to improve cyclic stability

Antimony-carbon nanocomposites are known anode materials for lithium- and sodium-ion batteries that can display an attractively stable cyclic behaviour in half-cells. They can also be used for potassium-ion batteries but a similar stability is not achieved, and electrode failure (abrupt capacity decay) is noted. Here, we probe the failure mechanism in potassium cells using samples with varied Sb particle sizes and weight fractions. A smaller particle size and extra carbon result in a failure in a later cycle. Mechanical degradation is the main reason for capacity drop; the phenomena associated with unstable solid electrolyte interphase are less critical. A number of strategies (an electrolyte additive, the type of a binder and adding an extra alloying element to composites) are explored. The choice of a binder affects the nature of decay and may lead to longer cycling. The inclusion of phosphorus in the nanocomposite coupled with an alternative binder appears to be more effective in improving the cyclic stability; a capacity of above 400 mAh g−1 is achieved in the first 50 cycles. The results demonstrate that the stability of alloying-dealloying anode materials in potassium-ion batteries can be influenced by optimising the composition of these materials and altering a binder.

The spatial footprint of injection wells in a global compilation of induced earthquake sequences.

Fluid injection can cause extensive earthquake activity, sometimes at unexpectedly large distances. Appropriately mitigating associated seismic hazards requires a better understanding of the zone of influence of injection. We analyze spatial seismicity decay in a global dataset of 18 induced cases with clear association between isolated wells and earthquakes. We distinguish two populations. The first is characterized by near-well seismicity density plateaus and abrupt decay, dominated by square-root space-time migration and pressure diffusion. Injection at these sites occurs within the crystalline basement. The second population exhibits larger spatial footprints and magnitudes, as well as a power law-like, steady spatial decay over more than 10 kilometers, potentially caused by poroelastic effects. Far-reaching spatial effects during injection may increase event magnitudes and seismic hazard beyond expectations based on purely pressure-driven seismicity.

Heart rate recovery fast-to-slow phase transition: Influence of physical fitness and exercise intensity.

Postexercise heart rate (HR) recovery presents an exponential decay, with two distinct phases: a fast phase, characterized by abrupt decay of HR, and determined by parasympathetic reactivation; and a slow phase, characterized by gradual decay of HR, and predominantly determined by sympathetic withdrawal. Although several methods have been proposed to assess postexercise HR recovery, none of those methods selectively assesses the time of transition from the fast to the slow phase of the HR recovery curve (HRRPT ), and the magnitude of decay prior to (HRRFP ) and after this point (HRRSP ). Therefore, the aim of the present study was to propose a method to identify HRRPT , HRRFP , and HRRSP and to verify the effects of exercise intensity and physical fitness on such parameters. Ten healthy young participants (24±3years; 23.6±1.7kg/m2 ) randomly underwent two exercise sessions (30min of cycling), at moderate (MI) and high intensity (HI); followed by 5min of inactive recovery. HR was continuously recorded during the sessions. The algorithm for HRRPT analysis was written in Python and is freely available online. HRRPT and HRRSP were increased in HI session compared with MI (81±24 vs. 60±20s; 8±10 vs. 1±5bpm; p=.04), and there was no difference in HRRFP between sessions (49±15 vs. 46±10bpm; p=.17). In addition, HRRPT for MI exercise session was significantly and negatively associated with VO2max (r=-0.85, p<.05). The method herein presented was sensitive to exercise intensity, and partially responsive to aerobic fitness. Next studies should perform the pharmacological and clinical validations of the method.

Abrupt dependence of ultrafast extrinsic photoconductivity on Er fraction in GaAs:Er

We present a study of room-temperature, ultrafast photoconductivity associated with a strong, sub-bandgap, resonant absorption around λ = 1550 nm in three MBE-grown GaAs epitaxial layers heavily doped with Er at concentrations of ≈2.9 × 1018 (control sample), 4.4 × 1020, and 8.8 × 1020 cm−3, respectively. Transmission-electron microscopy reveals lack of nanoparticles in the control sample, but abundant in the other two samples in the 1.0-to-3.0-nm-diameter range, which is consistent with the previously known results. We measure very high photoelectron (Hall) mobility (2.57 × 103 cm2/V-s) and terahertz power (46 μW average) in the 4.4 × 1020 sample, but then, an abrupt decay in these properties as well as the dark resistivity is seen as the Er doping is increased just 2 times. The Er doping has little effect on the picosecond-scale, 1550-nm photocarrier lifetime.

Reference-free path length interferometry of random media with the intensity moments analysis.

Stochastic interference of partially coherent light multiple scattered by a random medium is considered. The relationship between the second- and third-order moments of intensity fluctuations in random interference patterns, the coherence function of probe radiation, and the probability density of path differences for the interfering partial waves in the medium are established. The obtained relationships were verified using the statistical analysis of spectrally selected fluorescence radiation emitted by the laser-pumped dye-doped random medium. Rhodamine 6G water solution was applied as the doping agent for the ensembles of densely packed silica grains which were pumped by the CW radiation (532 nm) from the diode-pumped solid state laser. Experimentally observed abrupt decay of the second- and third-order moments of fluorescence intensity fluctuations for the wavelengths ranging from 620 nm to 680 nm is interpreted in terms of amplification of spontaneous emission at large dye concentrations. This paper discusses the new optical probe of random media defined as "the reference-free path length interferometry with the intensity moments analysis".

CFTR-mediated anion secretion across intestinal epithelium-like Caco-2 monolayer under PTH stimulation is dependent on intermediate conductance K+ channels

Parathyroid hormone (PTH), a pleiotropic hormone that maintains mineral homeostasis, is also essential for controlling pH balance and ion transport across renal and intestinal epithelia. Optimization of luminal pH is important for absorption of trace elements, e.g., calcium and phosphorus. We have previously demonstrated that PTH rapidly stimulated electrogenic [Formula: see text] secretion in intestinal epithelial-like Caco-2 monolayers, but the underlying cellular mechanism, contributions of other ions, particularly Cl- and K+, and long-lasting responses are not completely understood. Herein, PTH and forskolin were confirmed to induce anion secretion, which peaked within 1-3 min (early phase), followed by an abrupt decay and plateau that lasted for 60 min (late phase). In both early and late phases, apical membrane capacitance was increased with a decrease in basolateral capacitance after PTH or forskolin exposure. PTH also induced a transient increase in apical conductance with a long-lasting decrease in basolateral conductance. Anion secretion in both phases was reduced under [Formula: see text]-free and/or Cl--free conditions or after exposure to carbonic anhydrase inhibitor (acetazolamide), CFTR inhibitor (CFTRinh-172), Na+/H+ exchanger (NHE)-3 inhibitor (tenapanor), or K+ channel inhibitors (BaCl2, clotrimazole, and TRAM-34; basolateral side), the latter of which suggested that PTH action was dependent on basolateral K+ recycling. Furthermore, early- and late-phase responses to PTH were diminished by inhibitors of PI3K (wortmannin and LY-294002) and PKA (PKI 14-22). In conclusion, PTH requires NHE3 and basolateral K+ channels to induce [Formula: see text] and Cl- secretion, thus explaining how PTH regulated luminal pH balance and pH-dependent absorption of trace minerals.

Passive control of the flow around unsteady aerofoils using a self-activated deployable flap

ABSTRACTSelf-activated feathers are used by many birds to adapt their wing characteristics to the sudden change of flight incidence angle. In particular, dorsal feathers are believed to pop-up as a consequence of unsteady flow separation and to interact with the flow to palliate the sudden stall breakdown typical of dynamic stall. Inspired by the adaptive character of birds feathers, some authors have envisaged the potential benefits of using of flexible flaps mounted on aerodynamic surfaces to counteract the negative aerodynamic effects associated with dynamic stall. This contribution explores more in depth the physical mechanisms that play a role in the modification of the unsteady flow field generated by a NACA0020 aerofoil equipped with an elastically mounted flap undergoing a specific ramp-up manoeuvre. We discuss the design of flaps that limit the severity of the dynamic stall breakdown by increasing the value of the lift overshoot also smoothing its abrupt decay in time. A detailed analysis on the modification of the turbulent and unsteady vorticity field due to the flap flow interaction during the ramp-up motion is also provided to explain the more benign aerodynamic response obtained when the flap is in use.

New constraints on the most significant paleointensity change in Western Europe over the last two millennia. A non-dipolar origin?

Over the last years new evidences of several short-lived regional maxima of the geomagnetic field intensity at various times and locations have been defined. These features have important implications both for geomagnetic field modeling and for Earth's dynamo simulations. However, the nature, extent and underlying causes of these variations are still poorly understood. The major constraint for an adequate description of these important features is the absence of continuous detailed records and the current limited availability of precisely dated geomagnetic field recorders. In this context, archeological materials from superimposed strata covering long sequences of occupation provide a powerful tool to investigate the temporal variability of geomagnetic field strength at decadal and centennial time scales. In this work we report the archeomagnetic study of 79 potteries from Southeastern Spain collected in 14 different stratigraphic units. The chronological framework of the studied collection, ranging from the 9th to the 12th centuries, is based on historical/archeological data such as written sources and well-established typological and archeometric documentation on ceramics found on reference contexts in the area. Additionally, two radiocarbon dates obtained from two different stratigraphic units confirm the proposed chronological intervals. From classical Thellier and Thellier experiments including partial thermoremanent magnetization (pTRM) checks and TRM anisotropy and cooling rate corrections, height new high-quality mean intensities were derived. The new data provide an improved description of the sharp abrupt intensity decay that took place in Western Europe after the 800 AD intensity maximum, the most significant geomagnetic field intensity feature observed in Europe over the last two millennia. The new results confirm that several rapid intensity changes (with rates higher than 10 μT/century) took place in Western Europe during the recent history of the Earth. The comparison between the regional curve of Western Europe and the SHA.DIF.14k global field model predictions suggests that the 800 AD event observed in Europe is probably controlled by non-dipolar geomagnetic sources.

Caffeine Improved Time to Exhaustion But Did Not Change Alternative Maximal Accumulated Oxygen Deficit Estimated During a Single Supramaximal Running Bout.

The aim of the current study was to investigate the effects of acute caffeine supplementation on anaerobic capacity determined by the alternative maximal accumulated oxygen deficit (MAODALT) in running effort. Eighteen recreational male runners [29 ± 7years; total body mass 72.1 ± 5.8 kg; height 176.0 ± 5.4cm; maximal oxygen uptake (VO2max) 55.8 ± 4.2 ml·kg-1 ·min-1] underwent a graded exercise test. Caffeine (6 mg·kg-1) or a placebo were administered 1 hr before the supramaximal effort at 115% of the intensity associated with VO2max in a double-blind, randomized cross-over study, for MAODALT assessment. The time to exhaustion under caffeine condition (130.2 ± 24.5s) was 11.3% higher (p = .01) than placebo condition (118.8 ± 24.9 s) and the qualitative inference for substantial changes showed a very likely positive effect (93%). The net participation of the oxidative phosphorylation pathway was significantly higher in the caffeine condition (p = .02) and showed a likely positive effect (90%) of 15.3% with caffeine supplementation. The time constant of abrupt decay of excess postexercise oxygen consumption (τ1) was significantly different between caffeine and placebo conditions (p = .03) and showed a likely negative effect (90%), decreasing -8.0% with caffeine supplementation. The oxygen equivalents estimated from the glycolytic and phosphagen metabolic pathways showed a possibly positive effect (68%) and possibly negative effect (78%) in the qualitative inference with caffeine ingestion, respectively. However, the MAODALT did not differ under the caffeine or placebo conditions (p = .68). Therefore, we can conclude that acute caffeine ingestion does not modify the MAODALT, reinforcing the robustness of this method. However, caffeine ingestion can alter the glycolytic and phosphagen metabolic pathway contributions to MAODALT.

Calcareous microfossil-based orbital cyclostratigraphy in the Arctic Ocean

Abstract Microfaunal and geochemical proxies from marine sediment records from central Arctic Ocean (CAO) submarine ridges suggest a close relationship over the last 550 thousand years (kyr) between orbital-scale climatic oscillations, sea-ice cover, marine biological productivity and other parameters. Multiple paleoclimate proxies record glacial to interglacial cycles. To understand the climate-cryosphere-productivity relationship, we examined the cyclostratigraphy of calcareous microfossils and constructed a composite Arctic Paleoclimate Index (API) “stack” from benthic foraminiferal and ostracode density from 14 sediment cores. Following the hypothesis that API is driven mainly by changes in sea-ice related productivity, the API stack shows the Arctic experienced a series of highly productive interglacials and interstadials every ∼20 kyr. These periods signify minimal ice shelf and sea-ice cover and maximum marine productivity. Rapid transitions in productivity are seen during shifts from interglacial to glacial climate states. Discrepancies between the Arctic API curves and various global climatic, sea-level and ice-volume curves suggest abrupt growth and decay of Arctic ice shelves related to climatic and sea level oscillations.

Tropical cyclone activity in the northwestern Pacific associated with decaying Central Pacific El Niños

In this study, a comparative analysis was performed to reveal the relationship between the three types of temporal evolution of the Central Pacific (CP) El Nino (prolonged, abrupt, and symmetric decay) in the tropical Pacific Ocean and tropical cyclone (TC) activity in the Western North Pacific (WNP). TCs in the WNP were found to be sensitive to the different types of temporal evolution of the CP El Nino. During years of prolonged and symmetric decay, TCs were more frequent over East Asia with relatively strong TCs. In contrast, during years of abrupt decay, weak TCs with a relatively short lifespan more likely formed at slightly higher latitudes. The historical record of CP El Nino events is limited, but this study is expected to improve the understanding of complex natural systems and provide fundamental information for the scientific understanding and forecasting of TCs.

How well do climate models simulate atmospheric teleconnctions over the North Pacific and East Asia associated with ENSO?

During the El Nino and La Nina mature phase, atmospheric teleconnections over the North Pacific and East Asia vary considerably on sub-seasonal time scales, and are strongly phase-locked to the sub-seasonal evolution. In this study, we investigate how well climate models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulate the sub-seasonal evolution of teleconnections over the North Pacific and East Asia associated with El Nino-Southern Oscillation (ENSO). In the observations, there is a prominent anticyclone anomaly over the Kuroshio extension region (i.e. Kuroshio anticyclone), which significantly affects East Asian climate in the early winter (November–December) of El Nino years. However, in January, the Kuroshio anticyclone suddenly disappears, and a cyclonic flow dominates over the North Pacific. It is found here that the CMIP5 models simulate the overall extratropical teleconnection patterns, but they fail to reproduce some of these sub-seasonally-varying features in atmospheric circulation. For example, the models tend to simulate a weaker Kuroshio anticyclone in the early winter during El Nino phases, and fail to capture the abrupt decay of the Kuroshio anticyclone in the late winter. We demonstrate here that these systematic errors in ENSO teleconnection can be explained by systematic errors in tropical precipitation associated with ENSO. That is, negative precipitation anomalies over the western North Pacific (WNP) are too weak in the models compared to that in the observations, and their amplitude tends to be strengthened from December to the following January, while they are weakened in the observations. In addition, analyses on the inter-model diversity strongly support that relative magnitudes of WNP and central Pacific precipitation anomalies are critical for determining sub-seasonal evolution of ENSO teleconnections over the North Pacific and East Asia.

Degradation of volatile organic compounds in the gas phase by heterogeneous photocatalysis with titanium dioxide/ultraviolet light

This work presents an overview over heterogeneous photocatalysis performed in gas phase towards the degradation of o-xylene, n-hexane, n-octane, n-decane, methylcyclohexane and 2,2,4-trimethylpentane. The experimental set-up composed by a titanium plug flow reactor vessel contained a quartz tube with a 100 W UV lamp placed at center position from 1.7 cm to the quartz wall. A titanium dioxide film was immobilized on the internal walls of the reactor and used as catalyst. All measurements were taken after reaching steady state condition and evaluated at the inlet and outlet of the system. Conversion rates were studied in a wide range of residence times yielding to a 90% or above conversion as from 20 seconds of residence time. During experiments the temperature of reactor’s wall was monitored and remained between 52 and 62 °C. Temperature influence over degradation rates was negligible once a control experiment performed at 15 °C did not modify outgoing results. Humidity effect was also evaluated showing an ideal working range of 10 - 80% with abrupt conversion decay outside the range. By varying inlet concentration between 60 and 110 ppmv the VOC degradation curves remained unchanged. Loss over catalytic activity was only observed for o-xylene after 30 minutes of reaction, the catalyst was reactivated with a solution of hydrogen peroxide and UV light followed by additional deposition of the catalytic layer. The kinetic study suggests a first order reaction rate.Implications: The study of effective and economically viable techniques on the treatment of volatile organic compounds (VOCs) has being highlighted as an important parameter on the environmental research. The heterogeneous photocatalysis in gas phase was proved to be an effective process for the degradation of the nonaromatic VOCs tested, yielding high conversion values for the optimized systems.

Statistical Refinement and Fitting of Experimental Viscosity-to-Temperature Data in Ionic Liquids

The viscosity-to-temperature experimental data available in the open literature sources for 134 ionic liquids (ILs) was refined using a statistical procedure based on the confidence bands formalism. 1860 data points of 143 different references, among more than 2600 raw data points found in literature, were processed. As a result, 21% of the data set was rejected. The refined viscosity-to-temperature experimental data were successfully fitted to the η = f(T) Arrhenius-type equation with an R² correlation coefficient higher than 0.99 in all cases. Parameters A and B of the Arrhenius function for 134 ILs were given for the accurate estimation of viscosity in potential uses and compared to A and B parameters for 134 organic solvents. It was found that the obtained A and B values correlate linearly for the wide sample of 134 ionic liquids. As a consequence, it is concluded that ionic liquids having high viscosities at relatively low temperatures also exhibit an abrupt decay of the viscosity with the temperature. This A–B Arrhenius’ parameter relationship was also found in organic solvents, obtaining a regression line with a nearly identical slope but different intercept than that in the case of ILs. It indicated similar temperature dependence in the viscosity of ILs and organic compounds, but a differential higher viscosity of ionic fluids. In addition, it is observed that, for temperatures over 330–373 K, the viscosities of most ILs studied here are moderate, providing a potential range to manage this kind of solvent in practical applications with less transport property limitations.

Creation and Abrupt Decay of a Quasistationary Dark Soliton in a Polariton Condensate

We predict the existence of a self-localized solution in a nonresonantly pumped exciton-polariton condensate. The solution has a shape resembling the well-known hyperbolic tangent profile of a dark soliton, but exhibits several distinct features. We find that it performs small oscillations, which are transformed into ``soliton explosions'' at lower pumping intensities. Moreover, after hundreds or thousands of picoseconds of apparently stable evolution the soliton decays abruptly, which is explained by the acceleration instability found previously in the Bekki-Nozaki hole solutions of the complex Ginzburg-Landau equation. We show that the soliton can be formed spontaneously from a small seed in the polariton field or by using spatial modulation of the pumping profile.

Modeling ripple oscillations in the hippocampus

Sharp wave-ripples (SWRs) are highly synchronous network events displayed by the mammalian hippocampus during slow-wave sleep and immobile resting periods. A SWR event (~100 ms duration) is characterized by fast network oscillations (~200 Hz ripples) superimposed by a sharp wave, which is a large-amplitude, low-frequency (<10 Hz) signature in the local field potential of the hippocampal CA1 region. Such events are involved in memory consolidation. Understanding the mechanisms that give rise to SWRs can help us to gain insights on the computations being implemented during memory consolidation. Despite a large amount of electrophysiological data on SWRs in vivo (e.g. [1]) and in vitro (e.g. [2-4]) and many computational models (e.g. [5] and [6]), the basic mechanisms behind SWR generation remain elusive. Regarding the origin of the high-frequency ripple component during SWRs, two (not mutually exclusive) generative mechanisms have been proposed: First, a rhythmic output of a network of principal cells coupled by gap junctions, presumably between axons of pyramidal cells [5]. Second, an interneuron network coupled by chemical synapses that modulates the firing of pyramidal cells [6]. Modeling studies showed that both mechanisms can give rise to a prominent ripple component in the 200 Hz range. These two mechanisms could not only coexist but also be differentially expressed during SWR generation. Here we explore the oscillatory behavior of an in-silico model of a CA1 interneuron network to mimic in-vitro recordings from CA1 slices in which excitatory synaptic transmission is blocked and SWRs are induced by application of brief potassium puffs, which transiently excite neurons [3]. In such a preparation, the two proposed ripple generating mechanisms are decoupled and can be studied in isolation. Focusing on a model of a random interneuron network, we found that the power of ripple oscillations is stable for a wide range of the strength of the recurrent inhibitory coupling. A reduction of inhibitory conductance leads to a slight increase in network frequency, which is in line with [4]. Furthermore, larger reductions of inhibitory coupling leads to an abrupt decay of ripple power (see also [3]). Thus, some of the phenomenology of SWRs in vitro can be described in terms of chemical synaptic inhibition.

Case of the disappearing instanton

Instantons are tunneling solutions that connect two vacua, and under a small change in the potential, instantons sometimes disappear. We classify these disappearances as smooth (decay rate $\ensuremath{\rightarrow}0$ at disappearance) or abrupt (decay rate $\ensuremath{\ne}0$ at disappearance). Abrupt disappearances mean that a small change in the parameters can produce a drastic change in the physics, as some states become suddenly unreachable. The simplest abrupt disappearances are associated with annihilation by another Euclidean solution with higher action and one more negative mode; higher-order catastrophes can occur in cases of enhanced symmetry. We study a few simple examples, including the six-dimensional Einstein-Maxwell theory, and give a unified account of instanton disappearances.

A Simple Model for the Afternoon and Early Evening Decay of Convective Turbulence Over Different Land Surfaces

A simple model to study the decay of turbulent kinetic energy (TKE) in the convective surface layer is presented. In this model, the TKE is dependent upon two terms, the turbulent dissipation rate and the surface buoyancy fluctuations. The time evolution of the surface sensible heat flux is modelled based on fitting functions of actual measurements from the LITFASS-2003 field campaign. These fitting functions carry an amplitude and a time scale. With this approach, the sensible heat flux can be estimated without having to solve the entire surface energy balance. The period of interest covers two characteristic transition sub-periods involved in the decay of convective boundary-layer turbulence. The first sub-period is the afternoon transition, when the sensible heat flux starts to decrease in response to the reduction in solar radiation. It is typically associated with a decay rate of TKE of approximately t −2 (t is time following the start of the decay) after several convective eddy turnover times. The early evening transition is the second sub-period, typically just before sunset when the surface sensible heat flux becomes negative. This sub-period is characterized by an abrupt decay in TKE associated with the rapid collapse of turbulence. Overall, the results presented show a significant improvement of the modelled TKE decay when compared to the often applied assumption of a sensible heat flux decreasing instantaneously or with a very short forcing time scale. In addition, for atmospheric modelling studies, it is suggested that the afternoon and early evening decay of sensible heat flux be modelled as a complementary error function.