Small Pulse Research Articles

Experimental Investigation of the Machining Characteristics in Graphite-Powder-Mixed Electrochemical Discharge Machining of Microholes in Glass.

The effect of graphite powder on the machining characteristics in graphite-powder-mixed electrochemical discharge machining of microholes was still not clear. How the discharge mechanism changed with the addition of graphite powder into the electrolyte, which further led to changes in the morphology of the machined holes, remained to be revealed. In this study, a series of microhole machining experiments were conducted in glass. Comparisons of the discharge energy, microhole entrance diameter, hole taper, and tool electrode morphology after machining were made when machining in the electrolytes with and without graphite powder. Experimental results revealed that there were a lot of small pulse currents distributed on the current waveform when machining with the graphite-powder-mixed electrolyte. The average discharge energy of the small pulse current was 2.8 times as much as that of the general electrochemical discharge. After introducing graphite powder into the electrolyte, the entrance diameter of the hole became larger when the hole depth was deeper than 200 μm. The HAZ width increased with increasing hole depth at the voltage of 37-41 V, while it decreased at the voltage of 43 V. A reduction in hole taper angle with a range of 0.5° to 2.3° was achieved. In addition, after machining in electrolytes with and without graphite powder, the tool electrode surfaces showed different morphologies due to different discharges.

A new type of supercontinuum generation in hexagonal lattice C6H6-core PCF with broadband and low-power pump

Most of the spectral bandwidths of previous publications are still limited by high input powers making them economically less than ideal. By using a benzene core (C6H6) photonic crystal fiber (PCF) as a new supercontinuum (SC) light source, it is possible to achieve a very large spectral broadening with hundreds of times lower peak power. Due to the change in the diameter of air holes in the first ring near the core, near-zero flattened dispersion, high nonlinearity and small attenuation can be achieved for spectral broadening. The structural geometries of two C6H6-PCFs are optimized to generate wide SC at low input energy. The SC spectrum produced in 1[Formula: see text]cm long of all dispersion fiber extends from a part of visible light to the near-infrared range at 1.3[Formula: see text][Formula: see text]m wavelength and a small pulse energy of 18[Formula: see text]pJ (or 450[Formula: see text]W of electrical input). The second PCF shows wide soliton-induced SC from 0.8 to 4.2[Formula: see text][Formula: see text]m with 71[Formula: see text]pJ pulse energy (or input power approximately 790[Formula: see text]W) at 1.5[Formula: see text][Formula: see text]m wavelength within a fiber of 12[Formula: see text]cm. The proposed structures have the potential to become a new class of microstructured optical fibers for low-cost, broad-spectrum SC generation.

Postpartum Hemorrhage

Postpartum hemorrhage (PPH) is the primary cause of maternal mortality and morbidity worldwide: in fact, about a quarter of deaths that occur during pregnancy, childbirth or the puerperium are caused by postpartum hemorrhage. There are many causes of postpartum hemorrhage, the most important are: uterine atony, lacerations of the cervix and/or perineum, retention of placental material, coagulation problems, uterine inversion, uterine rupture. This causes of PPH are represented by the ‘4Ts’ formula: tone, tissue, trauma, thrombin. An important role is played by prevention: identification of risk factors, prophylaxis with oxytocin at the time of delivery, early treatment. The first important thing is the quantification of blood loss because the clinical signs are often blurred and due to frank anemia resulting in tachycardia, small and frequent pulse, hypotension, sweating, paleness. As previously mentioned, it is important to act early in the case of PPH through maintenance of velamina and targeted therapies that differ according to the cause of PPH (the 4T algorithm is useful). Early intervention reduces the need for blood transfusions and reduces the incidence of serious complications such as DIC. However, the management of postpartum hemorrhage is not limited to the postpartum phase, but the patient must be monitored in the puerperium, a phase in which the thromboembolic risk is increased. The couple must also be informed of the risk of PPH in future pregnancies. PPH represents a serious risk for the patient and requires multidisciplinary input and proper preparation of the team working in the delivery room.

The Brazilian semiarid region over the past 21,000 years: Vegetation dynamics in small pulses of higher humidity

In South America, one of the least addressed regions in paleoecological studies is the Brazilian Semiarid region, composed of vegetation from different biomes and currently marked by an arid climate. Although environmental conditions do not favor the formation of palynological sites, previous studies have indicated an expansion of savanna vegetation during the Last Glacial Maximum (LGM). However, more refined analyses with better spatial and temporal resolutions are important for a better understanding of these environments. The region's past reconstructed by models is related to intense climate changes on brief time scales in the Pleistocene and Holocene. Furthermore, paleoclimatic modeling reconstructions that only reproduce atmospheric conditions do not always represent all factors for vegetation formation and dynamics through time. In this work, we aimed to use the combination of bioclimatic and edaphic predictors to build models with machine learning algorithms capable of predicting the current and last 21,000 years' vegetation. Our results show that there is a significant gain in precision in the classification of vegetation formations when edaphic predictors are added. The use of subsurface horizons to generate edaphic attributes also resulted in better details of the local distribution of vegetation. The reconstruction of the past climate showed that the greatest change was promoted during the Heinrich Stadial 1 period; with the retraction of areas of open vegetation formations of the Hyperxerophilous Caatinga, areas of Arboreal Caatinga, Forested Caatinga, and Seasonal Deciduous Forest advanced. The current vegetation cover was established only in the Late Holocene, a period in which the humid conditions of the region allowed occupation by mostly dry vegetation.

An experimental study on switching waveform design with gate charge control for power MOSFETs

Designing switching waveforms is a technique for mitigating a trade-off between loss and noise in switching power devices. A novel and simple method has been proposed to compute the gate waveform to realize a designed switching waveform. The gate current pulse is calculated to eliminate the deviation between the designed target waveform and the observed waveform at the moment using a linear combination of drain-source voltage or drain current responses to a small gate charge pulse train. In this paper, a verification system including a simple gate current pulse generator consisting of operational amplifiers and transistors was built together with a conventional voltage source gate driver, and validation of the proposed method was experimentally performed using the drain-source voltage waveform of a Si MOSFET during the turn-off phase. Applying the obtained drain-source voltage responses to the proposed method, the gate current pulse to be added to realize a given target waveform was calculated and superimposed on the output of the gate driver. The measured drain-source voltage waveform was well-matched to the target. In addition, the impact of the drain current values on the design of the drain-source waveform was verified.

Inhibition of Dust Re-Deposition for Filter Cleaning Using a Multi-Pulsing Jet

The re-deposition of detached dust during online pulse-jet cleaning is an important issue encountered during filter regeneration. To reduce dust re-deposition, multi-pulsing jet cleaning schemes were designed and experimentally tested. A pilot-scale pulse-jet cleaning dust collector was built with one vertically installed pleated filter cartridge. The effects of pulse duration and interval on the pulse pressure were tested, and the dust re-deposition rate and mechanism were studied and analyzed. It was found that, for the single-pulsing jet, the pulse duration had a critical value of approximately 0.080 s in this test, above which the pulse pressure remained at approximately 0.75 kPa and did not increase further. For the multi-pulsing jet with a small pulse interval (less than approximately 0.10 s), the pulse flows superimposed and reached a higher pulse pressure with a slight inhibition of dust re-deposition. For the multi-pulsing jet with a long pulse interval (over 0.15 s), dust re-deposition was clearly inhibited. The re-deposition rate decreased from 63.8% in the single-pulsing scheme to 24.4% in the multi (five)-pulsing scheme with the same total pulse duration of 0.400 s. The multi-pulsing scheme lengthens the duration of reverse pulse flow, resulting in more elapsed time for the detached dust to freely fall, and inhibiting the re-deposition of dust. The elapsed time in the five-pulsing jet scheme with the recommended pulse duration of 0.080 s and interval of 0.25 s was 2.8 times higher than that of the single-pulsing jet with the same total pulse duration.

Static and dynamic magnetic characteristics in concentric permalloy nanorings

Magnetic nanodisks and nanorings have been focus of attention for quite some time due to their applicability in magnetic memory devices. In this paper, static and dynamic magnetic properties of Permalloy concentric thin ring nanostructures are reported as a function of the number of rings by using micromagnetic simulations. The maximum outer radius (R) and thickness (t) of the concentric rings are fixed at 100 nm and 20 nm respectively. The distance between any two neighbouring rings is always maintained equal to the width of each ring while the number of nanorings is increased starting from one to five. In-plane magnetic hysteresis loops show that in all cases, the remanence and coercivity values are found to be almost zero while vortex state is exhibited with opposite helicity in adjacent nanorings. When the number of nanorings reach five, the narrowest hysteresis loop is observed with almost no hysteresis at all. Dynamic susceptibility spectra was computed by relaxing the system from a out of plane saturated state followed by an in-plane excitation using a small field pulse. In most of the cases, the in plane magnetic field pulse excites azimuthal spin wave modes. The resonance frequency corresponding to these excitation modes depends on the remanent configuration and the number of peaks increase with increment in the number of rings. The ferromagnetic resonance mode that is common for all the samples considered, moves towards lower frequency with increase in number of concentric rings.

Dynamics of short-term ecosystem carbon fluxes induced by precipitation events in a semiarid grassland

Abstract. Infrequent and small precipitation (PPT) events characterize PPT patterns in semiarid grasslands; however, plants and soil microorganisms are adapted to use the unpredictable small pulses of water. Several studies have shown short-term responses of carbon and nitrogen mineralization rates (called the “priming effect” or the Birch effect) stimulated by wet–dry cycles; however, dynamics, drivers, and the contribution of the priming effect to the annual C balance are poorly understood. Thus, we analyzed 6 years of continuous net ecosystem exchange measurements to evaluate the effect of the PPT periodicity and magnitude of individual PPT events on the daily/annual net ecosystem C exchange (NEE) in a semiarid grassland. We included the period between PPT events, previous daytime NEE rate, and previous soil moisture content as the main drivers of the priming effect. Ecosystem respiration (ER) responded within a few hours following a PPT event, whereas it took 5–9 d for gross ecosystem exchange (GEE; where −NEE = GEE + ER) to respond. Precipitation events as low as 0.25 mm increased ER, but cumulative PPT > 40 mm infiltrating deep into the soil profile stimulated GEE. Overall, ER fluxes following PPT events were related to the change in soil water content at shallow depth and previous soil conditions (e.g., previous NEE rate, previous soil water content) and the size of the stimulus (e.g., PPT event size). Carbon effluxes from the priming effect accounted for less than 5 % of ecosystem respiration but were significantly high with respect to the carbon balance. In the long term, changes in PPT regimes to more intense and less frequent PPT events, as expected due to the effects of climate change, could convert the semiarid grassland from a small C sink to a C source.

Analysis of electro-optically adjustable cascaded second-order nonlinearity in tapered BBO crystal: a compression scheme for ultra-short pulse

In this analytical approach, electro-optically tunable second-order cascaded nonlinearity was targeted to investigate the potential of ultrashort pulse compression in a tapering nonlinear medium. The proposed framework is ideally suited to generating high-intensity pulses with small pulse widths by exploiting second-harmonic generation and the electro-optic effect in a bulk beta-barium borate with exceptional optical advantages. Considering both linear and nonlinear absorption losses, the necessary and sufficient conditions for the compression of ultrashort pulses were developed using the generalized nonlinear Schrödinger equation. In agreement with simulations, an attempt is made to compress an optical pulse from 120 to 39 fs using an external voltage of ∓5.69 KV, which leads to a phase mismatch ( Δk ) = ± 124.8 m − 1, a phase shift ( ΔϕNL ) = ± 1.26π, and an effective cascaded refractive index (n2cascade)=±3.371×10−20 m2/W. The results suggest that the technology developed in this study will open the door to a plethora of applications, including fields as diverse as laser surgery, range finding through LIDAR, and many more.

An improved algorithm for design of broadband excitation, inversion, and mixing pulse sequences by iterative optimization of phases: TOPS-2

This paper presents an improved iterative algorithm (TOPS-2) for the design of broadband inversion, excitation and coherent transfer mixing sequence (TOCSY) pulses. The evolution of the Bloch vector is presented as a sequence of small constant flip angle pulses with varying phases and constant amplitude. This paper describes an improved algorithm for iterative optimization of piece-wise constant phases as we incorporate the quadratic terms in the propagators. In our iterative optimization we obtain a closed-form expression for each phase, and these phases are optimized sequentially using the new improved algorithm. This paper compares the simulation results of the TOPS vs TOPS-2 and shows that TOPS-2 perform better. Experimental validation of excitation and inversion TOPS-2 pulse sequence is performed with .5% H2O in 99.5% D2O, and experimental validation of TOPS-2 mixing (TOCSY) pulse sequence is done with 0.1% of Ethylbenzene (EB) in CDCl3 solvent.

Momentum spirals in multiphoton pair production revisited

Spirals in multiphoton pair production are revisited by two counter-rotating fields with time delay for different cycles in pulse. Novel findings include that for subcycle fields, the remarkable spiral structure in the momentum spectrum can be still caused by a large time delay compared to the previous study for supercycle case where it is easier to be generated by a small time delay. And also there exist a range of critical polarization values for the spirals appearance corresponding to the different cycle number. The relative phase difference between two fields causes not only severe symmetry breaking of the momentum spectra pattern and spiral, but also a significant change for the shape and the number of spiral arm. Upon the number density, it is found a more sensitive to the cycle number, in particularly, it is enhanced by more than one order of magnitude for small cycle pulse, while it is increased about few times when the time delay is small. These results provide an abundant theoretical testbed for the possible experimental observation on the multiphoton pair production in future. Meanwhile, it is applicable to regard the particles momentum signatures as a new probing to the laser field information with it from the vacuum.

Post-ischemic reorganization of sensory responses in cerebral cortex.

Sensorimotor integration is critical for generating skilled, volitional movements. While stroke tends to impact motor function, there are also often associated sensory deficits that contribute to overall behavioral deficits. Because many of the cortico-cortical projections participating in the generation of volitional movement either target or pass-through primary motor cortex (in rats, caudal forelimb area; CFA), any damage to CFA can lead to a subsequent disruption in information flow. As a result, the loss of sensory feedback is thought to contribute to motor dysfunction even when sensory areas are spared from injury. Previous research has suggested that the restoration of sensorimotor integration through reorganization or de novo neuronal connections is important for restoring function. Our goal was to determine if there was crosstalk between sensorimotor cortical areas with recovery from a primary motor cortex injury. First, we investigated if peripheral sensory stimulation would evoke responses in the rostral forelimb area (RFA), a rodent homologue to premotor cortex. We then sought to identify whether intracortical microstimulation-evoked activity in RFA would reciprocally modify the sensory response. We used seven rats with an ischemic lesion of CFA. Four weeks after injury, the rats' forepaw was mechanically stimulated under anesthesia and neural activity was recorded in the cortex. In a subset of trials, a small intracortical stimulation pulse was delivered in RFA either individually or paired with peripheral sensory stimulation. Our results point to post-ischemic connectivity between premotor and sensory cortex that may be related to functional recovery. Premotor recruitment during the sensory response was seen with a peak in spiking within RFA after the peripheral solenoid stimulation despite the damage to CFA. Furthermore, stimulation in RFA modulated and disrupted the sensory response in sensory cortex. The presence of a sensory response in RFA and the sensitivity of S1 to modulation by intracortical stimulation provides additional evidence for functional connectivity between premotor and somatosensory cortex. The strength of the modulatory effect may be related to the extent of the injury and the subsequent reshaping of cortical connections in response to network disruption.

Ultrafast pulse pumping of topological nanospaser

We theoretically examine a topological nanospaser that is optically pumped using an ultra-fast circularly-polarized pulse. The spasing system consists of a silver nanospheroid, which supports surface plasmon (SP) excitations, and a transition metal dichalcogenide (TMDC) monolayer nanoflake. The silver nanospheroid screens the incoming pulse and creates a non-uniform spatial distribution of electron excitations in the TMDC nanoflake. These excitations decay into the localized SPs, which can be of two types with the corresponding magnetic quantum number ±1. The amount and the type of the generated SPs depend on the intensity of the optical pulse. For small pulse amplitude, only one plasmonic mode is predominantly generated, resulting in far-field elliptically polarized radiation. For large amplitude of the optical pulse, both plasmonic modes are generated in almost the same amount, resulting in linearly polarized far-field radiation.

Formulating finger millet (Eleusine coracana L) and cowpea (Vigna unguiculata) food blend for enhanced micronutrients for children below 5 years

Malnutrition of children under 5 years is a public health concern because it is the most vulnerable stage of child’s growth where its impact results in long term health conditions such as stunting, wasting, obesity and poor cognitive development. This study aimed at developing a Rapoko-Cowpea porridge blend to enhance dietary micronutrients among children below the age of 5 years and assess its sensory acceptability. A mixed methods research approach was adopted consisting of a quasi- experiment and a cross sectional survey. Vendors from Mbare market were clustered based on the source of their finger millet and cowpea grains (Masvingo, Murewa, Gokwe). A Completely Randomised Design (CRD) was used with three treatments (blends) replicated three times. Proximate analysis was done using standard AOAC methods. Compared to cowpea, finger millet had the highest levels of carbohydrates (78.12g/100g), iron (8.7mg/100g), zinc (3.77mg/100g). Results also show that 75:25. Rapoko-Cowpea blend ratio had the ability to meet WHO daily nutrient requirements for children under the age of 5 years. Blend ratio of Rapoko: cowpeas (75:25) had the highest carbohydrates (69.41g/100g), protein (25.64g/100g), zinc (1.74mg/100g), iron (5.14mg/100g), energy (411.37kcal), and vitamins (0.11 mcg RAE) with RaCoB1 blend having the lowest nutrient composition. Results have showed that finger millet (Rapoko), cowpeas and RaCoB (Rapoko-Cowpea blend) blends have high macro and micronutrients (iron and zinc) to support daily nutritional requirements of children below the age of 5 years and may help in addressing malnutrition. Sensory evaluation was done with 100 panellists from the University of Zimbabwe and of the three blends, a 75:25 ratio was the most preferred (90.88%). Further studies need to analyse the effects of anti-nutritional factors, bioavailability of nutrients, shelf life of the food blend and commercialization potential of RaCoB blends. The government is therefore encouraged to provide agronomic support for increased productivity of small grains and pulses through improved research and extension. There is a need to develop a policy at national level that promotes blending of cereals and pulses as well as innovative small scale food processing initiatives through private-public partnerships. Key words: Children under 5 years, Cowpea, food blending, Malnutrition, Micronutrients, Rapoko, Sensory evaluation

Revealing Main Reaction Paths to Olefins and Aromatics in Methanol-to-Hydrocarbons over H-ZSM-5 by Isotope Labeling

The nature of hydrocarbon pool (HCP) intermediates in the methanol-to-hydrocarbons (MTH) process has been thoroughly investigated, especially for BEA- and CHA-type zeolite catalysts like H-β and H-SAPO-34. Herein, we further reveal the dynamic mechanistic details of the MTH process over the H-ZSM-5 catalyst at 400 °C, based on the dual-cycle mechanism and HCP in this medium-pore zeolite. Application of switching sequences of 13C-labeled and unlabeled methanol pulses over a model H-ZSM-5 catalyst combined with on-line MS analysis and a recently reported technique called “fast scanning-pulse GC analysis” provides a direct and quantitative insight into the MTH reactions under quasi-steady-state conditions. The transient product responses showed the almost instant formation of hydrocarbons upon a small pulse of methanol, followed by secondary formation of light aromatics via HCP decomposition and olefin alkylation–dealkylation, especially in a long catalyst bed when methanol is quickly consumed in the initial reaction zone in the catalyst bed. The isotopic analysis of typical aliphatic C3+ product responses after switching 13C-methanol pulses to the unlabeled methanol pulses showed a fast isotope scrambling in the formation of C3+ species. MS analysis of the light aromatics indicates a complete consecutive but slower isotope incorporation process of 12C into 13C-aromatics. Results provide direct experimental confirmation of the kinetically preferred olefin-based cycle over the aromatic-based cycle. The sequential isotopic incorporation strongly suggests that the paring reaction pathway through aromatic ring contraction and re-expansion steps is operative. In the appearance of aromatics upon pulsing methanol over larger catalyst beds, four processes are directly discerned, involving the displacement of adsorbed species by formed water, isotope incorporation yielding directly labeled and unlabeled products through the paring mechanism and direct aromatization, and HCP conversion through secondary reactions.

Investigations of fracture behavior and pore structure change in pulse fracturing for cement block

Pulse fracturing can reduce fracture initiation pressure and increase stimulation effectiveness. To investigate the effect of frequency and amplitude on fracture propagation behavior in pulse fracturing, tri-axial experiments with acoustic emission (AE) monitoring are applied. The results demonstrate that pulse fracturing can generate mixed mode fractures, and the distinct deviation of the fracture propagation near-wellbore can be seen for pulse fracturing. Both pulse frequency and amplitude are critical parameters for the propagation path, measured AE accounts, accumulative energy and pore connectivity. The increase in amplitude is beneficial for large fracturing energy, but the increase in frequency is not necessarily helpful for fracture effectiveness. The harmony between the rock and pump frequency can yield the largest acoustic events and pore connectivity. The pore structure and microfracture change of rock before and after pulse fracturing at different distances are measured with nuclear magnetic resonance (NMR) and CT scans, indicating that pulse fracturing has a strong capability to create a larger stimulated area than the monotonic fracturing model. In addition, obvious microfracture generation and pore space expansion can be seen near the injection port. However, the pore structure comparison indicates that the pulse fracturing mode mainly improves the scale of macropores, which is primarily because of the relatively small pulse fracturing parameters used in these experiments. Thus, this study provides an understanding of pulse frequency and amplitude effects for stimulation effectiveness related to pulse fracturing of tight reservoirs.

A Compact Repetitive Marx Generator for Generating Intense Electron Beams for HPM Sources

A 500 kV, 80 Hz repetition rate compact Marx generator has been designed and developed for producing high intense relativistic electron beams for high-power microwave (HPM) sources. This Marx generator comprises eight bipolar stages (16 stages of unipolar) using energy storage capacitors for achieving improved performance in repetition mode operation. The maximum charging voltage per stage is 50 kV, producing an erected voltage of 800 kV. However, the load voltage will vary according to the impedance of the load connected across the generator. Custom-designed energy storage capacitors were developed to allow voltage reversal of up to 30%–50%, enabling the system to deliver a higher current. A small pulse transformer-based triggering unit with an output voltage of 30 kV was used for triggering the generator. The system’s performance was tested in pulse repetition frequency (PRF) mode with resistive and diode loads and achieved a repetition rate of 80 Hz. An energy density of ~460 J/m3 was achieved in the developed system. A vircator device was connected and tested to benchmark the Marx generator for its repetitive and burst mode operations. The test results show the measured RF output power of 100 MW.

Early Miocene (Burdigalian) Dinoflagellate Cysts from the Kerala Basin, Southwest India: Indicators of Marine Ingression at the Onset of the Mid-Miocene Climate Optimum (MMCO)

Abstract In the present study, the assemblages of organic walled dinoflagellate cyst (dinocysts) and calcareous nannofossils from Quilon Formation, Kerala Basin, south-western India are analyzed for age interpretation and reconstruction of the depositional environment. The integrated biostratigraphy based on dinocysts and calcareous nannofossils from the same sediment samples indicates that the studied succession was deposited during the early Miocene (middle Burdigalian, ~19-17.5 Ma) time. The dinocyst assemblages contain abundant taxa (Cleistosphaeridium, Polysphaeridium, Lingulodinium, Homotryblium and Spiniferites) that range from shallow inner to outer neritic marine zone. The abundance of autotrophic, thermophilic taxa suggests relatively high surface water temperatures and high nutrient availability. The dinocyst assemblage in the lower part of the studied succession is dominated by Cleistosphaeridium spp., Polysphaeridium spp., Spiniferites spp., Homotryblium spp. and Lingulodinium spp. An increase in the relative abundances of outer neritic dinocyst taxa such as Spiniferites, Achomosphaera and Hystrichokolpoma in the upper part of the succession suggests a change towards more open marine conditions created during marine ingression. The interpreted marine ingression along the south-western Indian coast probably corresponds to the initial small pulses of transgression at the onset of the long-term global sea-level maximum related to the Mid-Miocene Climatic Optimum (MMCO).

Six years of fluvial response to a large dam removal on the Carmel River, California, USA

AbstractMeasuring river response to dam removal affords a rare, important opportunity to study fluvial response to sediment pulses on a large field scale. We present a before–after/control–impact study of the Carmel River, California, measuring fluvial geomorphic and grain‐size evolution over 8 years, six of which postdated removal of a 32 m‐high dam (one of the largest dams removed worldwide) and included 11 flow events exceeding the 2‐year flood magnitude. We find that the reservoir‐sediment pulse following dam removal was relatively small (97 000 ± 24 000 t over 4 years), owing to deliberate reservoir‐sediment stabilization. Scaled to the size of the Carmel River watershed and compared against long‐term bedrock denudation rates, the post‐dam‐removal sediment release was slightly less than the annualized long‐term sediment export from this basin. New sediment transited >30 km to the river mouth in less than 2 years, assisted by floods 2 and 4 years after dam removal. The sediment pulse fined the downstream riverbed while causing mostly low‐magnitude bed‐elevation changes: commonly 0.5 to 1 m or smaller, occurring as discontinuous sediment patches or interstitial deposits, aside from the filling and subsequent partial scour of deep pools. There was no major geomorphic reset downstream from the dam site. Geomorphic changes were driven almost entirely by flow rather than by the modest increase in sediment supply, in contrast to recent examples from other large dam removals. The relatively minor disturbance caused by dam removal on the Carmel River is likely analogous to many future dam removals: a relatively small sediment pulse after deliberate limitation of reservoir‐sediment erosion, and with an upstream dam remaining in place. Thus, a large dam removal need not lead to major downstream impacts.

Positive pressure therapy for Ménière's disease.

Ménière's disease is a condition that causes recurrent episodes of vertigo, associated with hearing loss and tinnitus. It is often treated with medication, but different interventions are sometimes used. Positive pressure therapy is a treatment that creates small pressure pulses, generated by a pump that is attached to tubing placed in the ear canal. It is typically used for a few minutes, several times per day. The underlying cause of Ménière's disease is unknown, as is the way in which this treatment may work. The efficacy of this intervention at preventing vertigo attacks, and their associated symptoms, is currently unclear. To evaluate the benefits and harms of positive pressure therapy versus placebo or no treatment in people with Ménière's disease. The Cochrane ENT Information Specialist searched the Cochrane ENT Register; CENTRAL; Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished trials. The date of the search was 14 September 2022. We included randomised controlled trials (RCTs) and quasi-RCTs in adults with a diagnosis of Ménière's disease comparing positive pressure therapy with either placebo or no treatment. We excluded studies with follow-up of less than three months. DATA COLLECTION AND ANALYSIS: We used standard Cochrane methods. Our primary outcomes were: 1) improvement in vertigo (assessed as a dichotomous outcome - improved or not improved), 2) change in vertigo (assessed as a continuous outcome, with a score on a numerical scale) and 3) serious adverse events. Our secondary outcomes were: 4) disease-specific health-related quality of life, 5) change in hearing, 6) change in tinnitus and 7) other adverse effects. We considered outcomes reported at three time points: 3 to < 6 months, 6 to ≤ 12 months and > 12 months. We used GRADE to assess the certainty of evidence for each outcome. MAIN RESULTS: We included three studies with a total of 238 participants, all of which compared positive pressure using the Meniett device to sham treatment. The duration of follow-up was a maximum of four months. Improvement in vertigo A single study assessed whether participants had an improvement in the frequency of their vertigo whilst using positive pressure therapy, therefore we are unable to draw meaningful conclusions from the results. Change in vertigo Only one study reported on the change in vertigo symptoms using a global score (at 3 to < 6 months), so we are again unable to draw meaningful conclusions from the numerical results. All three studies reported on the change in the frequency of vertigo. The summary effect showed that people receiving positive pressure therapy had, on average, 0.84 fewer days per month affected by vertigo (95% confidence interval from 2.12 days fewer to 0.45 days more; 3 studies; 202 participants). However, the evidence on the change in vertigo frequency was of very low certainty, therefore there is great uncertainty in this estimate. Serious adverse events None of the included studies provided information on the number of people who experienced serious adverse events. It is unclear whether this is because no adverse events occurred, or whether they were not assessed and reported. AUTHORS' CONCLUSIONS: The evidence for positive pressure therapy for Ménière's disease is very uncertain. There are few RCTs that compare this intervention to placebo or no treatment, and the evidence that is currently available from these studies is of low or very low certainty. This means that we have very low confidence that the effects reported are accurate estimates of the true effect of these interventions. Consensus on the appropriate outcomes to measure in studies of Ménière's disease is needed (i.e. a core outcome set) in order to guide future studies in this area and enable meta-analyses of the results. This must include appropriate consideration of the potential harms of treatment, as well as the benefits.